Guidelines for the Construction of Polar Class Ships

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Rules for Classification and Construction I Ship Technology

1 Seagoing Ships

22 Guidelines for the Construction of Polar Class Ships

Edition 2008

The following Guidelines come into force on November 1st, 2008

Germanischer Lloyd Aktiengesellschaft

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Published by: Germanischer Lloyd Aktiengesellschaft, Hamburg Printed by: Gebrüder Braasch GmbH, Hamburg I - Part 1 Table of Contents Chapter 22 GL 2008 Page 3

Table of Contents

Section 1 Polar Class Descriptions and Application A. Application ...... 1- 1 B. Polar Class Notations ...... 1- 1 C. Upper and Lower Ice Waterlines ...... 1- 1

Section 2 Structural Requirements A. Scope ...... 2- 1 B. Hull Areas ...... 2- 1 C. Design Ice Loads ...... 2- 2 D. Shell Plate Requirements ...... 2- 5 E. Framing - General ...... 2- 6 F. Framing - Transversely Framed Side Structures and Bottom Structures ...... 2- 7 G. Framing - Side Longitudinals (Longitudinally Framed Ships) ...... 2- 8 H. Framing - Web Frame and Load-Carrying Stringers ...... 2- 9 I. Framing - Structural Stability ...... 2- 9 J. Plated Structures ...... 2- 10 K. Corrosion/Abrasion Additions and Steel Renewal ...... 2- 10 L. Materials ...... 2- 10 M. Longitudinal Strength ...... 2- 12 N. Stem and Stern Frames ...... 2- 14 O. Appendages ...... 2- 14 P. Local Details ...... 2- 14 Q. Direct Calculations ...... 2- 15 R. Welding ...... 2- 15

Section 3 Machinery Requirements A. General ...... 3- 1 B. Materials ...... 3- 1 C. Design Principles ...... 3- 2 D. Propeller ...... 3- 2 E. Shafting ...... 3- 9 F. Gears, Flexible Couplings, Clutches ...... 3- 13 G. Azimuth Propulsors ...... 3- 14 H. Prime Movers ...... 3- 15 I. Auxiliary Systems ...... 3- 15 J. Foundation of Equipment ...... 3- 17 K. Alternative Design ...... 3- 17

Annex A Load Cases for Open and Ducted Propellers

Annex B Quality Requirements for FEM Analysis A. Requirements for FE Model ...... B- 1 B. Good Engineering Practice for FE Analysis ...... B- 1 C. Boundary Conditions ...... B- 1

I - Part 1 Section 1 C Polar Class Descriptions and Application Chapter 22 GL 2008 Page 1–1

Section 1

Polar Class Descriptions and Application

A. Application designers and administrations in selecting an appropriate Polar Class for safe operation. The level of 1. These Guidelines apply to ships constructed propulsion power shall be based on voyage profile and of steel and intended for navigation in polar ice- anticipated ice conditions. covered waters. They are based on the IACS Unified Requirements I1, I2 and I3 (Corr. 1 Oct 2007). 2. Ships the ice-strengthening of which com- plies with Sections 2 and 3 of these Guidelines will Notes have the Notations PC7, PC6, PC5, PC4, PC3, PC2 or PC1 affixed to their Character of Classification. Reference is made to the IMO Guidelines for Ships Where the hull or machinery is strengthened for a Operating in Arctic Ice-Covered Waters (MSC / Circ. higher Polar Class Notation, a corresponding entry 1056, MEPC / Circ.399, 23 December 2002). will be made in the Technical File to the Class Certifi- Ships intended to operate in the arctic waters of Can- cate. For PC7 or PC6 ships requiring E3 or E4 ada are to comply with the Canadian Arctic Shipping equivalency (see Chapter 1 – Hull Structures, Section Pollution Prevention Regulations. GL is authorised to 15.A.), the engine output requirements of Chapter 1 – issue the relevant Arctic Pollution Prevention Certifi- Hull Structures, Section 15.A.3. need also to be ob- cate. served.

3. Ships which beyond the requirements for the Polar Class Notations PC7 to PC1 have been specially B. Polar Class Notations designed for escort or ice management functions, having powering and dimensions that allow it to un- 1. Polar Class Notations are used throughout dertake aggressive operations in ice-covered waters, these Guidelines to convey differences between clas- will in addition have the Notation ICEBREAKER ses with respect to operational capability and strength. affixed to their character of classification. Dimension- It is the responsibility of the owner to select an appro- ing of the structure and machinery with regard to the priate Polar Class and level of propulsion power. The foreseen area of operation has to be agreed with GL. descriptions in Table 1.1 are intended to guide owners, 4. If the scantlings required by these Guidelines Table 1.1 Polar Class Descriptions are less than those required for ships without ice- strengthening, the scantlings required by the latter are Polar Ice description to be maintained. Class (based on WMO Sea Ice Nomenclature)

PC1 Year-round operation in all polar waters C. Upper and Lower Ice Waterlines Year-round operation in moderate multi-year PC2 ice conditions 1. The upper ice waterline (UIWL) is the high- Year-round operation in second-year ice PC3 est waterline on which the ship is intended to operate which may include multi-year ice inclusions in polar ice-covered waters. Year-round operation in thick first-year ice PC4 which may include old ice inclusions 2. The lower ice waterline (LIWL) is the lowest waterline on which the ship is intended to operate Year-round operation in medium first-year PC5 in polar ice-covered waters and is to be determined ice which may include old ice inclusions with due regard to the vessel's ice-going capability in Summer/autumn operation in medium first- ballast loading conditions (e.g. propeller submer- PC6 year ice which may include old ice inclu- gence). sions 3. The maximum and minimum draughts fore, Summer/autumn operation in thin first-year PC7 ice which may include old ice inclusions amidships and aft will be stated in the Technical File

to the Class Certificate.

I - Part 1 Section 2 B Structural Requirements Chapter 22 GL 2008 Page 2–1

Section 2

Structural Requirements

A. Scope B. Hull Areas

1. The contents of this Section provide require- 1. The hull of all Polar Class ships is divided ments for the structural arrangements of Polar Class into areas reflecting the magnitude of the loads that ships. Each area of the hull and all appendages shall be are expected to act upon them. In the longitudinal strengthened to resist the global and local ice loads, as direction, there are four regions: Bow (B), Bow Inter- well as temperature, characteristic of their Polar Class. mediate (BI), Midbody (M) and Stern (S). The Bow Note Intermediate, Midbody and Stern regions are further divided in the vertical direction into the Bottom (b), Reference is made to the GL Rules Chapter 1 – Hull Lower (l) and Ice belt (i) regions. The extent of each Structures, Section 3 and Part A (Construction Provi- hull area is illustrated in Fig. 2.1. sions) of the IMO Guidelines for Ships Operating in Arctic Ice-Covered Waters (MSC / Circ. 1056, MEPC/ Circ. 399, 23 December 2002) for additional guidance 2. The upper ice waterline (UIWL) and lower concerning structural arrangements. ice waterline (LIWL) are as defined in Section 1, C.

Fig. 2.1 Hull area extents Chapter 22 Section 2 C Structural Requirements I - Part 1 Page 2–2 GL 2008

3. Fig. 2.1 notwithstanding, at no time shall the ses PC6 and PC7, the ice load parameters are functions boundary between the Bow and Bow Intermediate of the actual bow shape. To determine the ice load regions be forward of the intersection point of the line parameters (Pavg, b and w), it is necessary to calculate of the stem and the ship baseline. the following ice load characteristics for sub-regions of the Bow area; shape coefficient (fai), total glancing 4. Fig. 2.1 notwithstanding, the aft boundary of impact force (Fi), line load (Qi) and pressure (Pi). the Bow region need not be more than 0,45 L aft of the forward perpendicular (FP) 1.4 In other ice-strengthened areas, the ice load L = ship length as defined in Chapter 1 – Hull Struc- parameters (Pavg, bNonBow and wNonBow) are deter- tures, Section 1, H.2.1, but measured on the upper ice mined independently of the hull shape and based on a waterline (UIWL) [m] fixed load patch aspect ratio, AR = 3,6.

5. The boundary between the Bottom and 1.5 Design ice forces calculated according to 2. Lower regions is to be taken at the point where the are in general considered valid for bow regions where shell is inclined 7° from horizontal. the frame angle β is greater than or equal to 1,3 times the waterline angle α (see Fig. 2.2). Design ice forces 6. If a ship is intended to operate astern in ice for other bow regions are to be specially considered. regions, the aft section of the ship shall be designed using the Bow and Bow Intermediate hull area re- 1.6 Ship structures that are not directly subjected quirements. to ice loads may still experience inertial loads of stowed cargo and equipment resulting from ship/ice 7. All hull areas, including the locations of the interaction. These inertial loads, calculated according UIWL and LIWL, are to be clearly indicated on the to the design accelerations specified in Section 3, J.2. shell expansion submitted for approval. to J.4., are to be considered in the design of these structures.

2. Glancing impact load characteristics C. Design Ice Loads The parameters defining the glancing impact load 1. General characteristics are reflected in the class factors listed in Table 2.1. 1.1 For ships of all Polar Classes, a glancing impact on the bow is the design scenario for determin- 2.1 Bow Area ing the scantlings to resist ice loads. 2.1.1 In the Bow area, the force (F), line load (Q), 1.2 The design ice load is characterized by an pressure (P) and load patch aspect ratio (AR) associ- average pressure (Pavg) uniformly distributed over a ated with the glancing impact load scenario are func- rectangular load patch of height (b) and width (w). tions of the hull angles measured at the upper ice waterline (UIWL). The influence of the hull angles is 1.3 Within the Bow area of all Polar Classes, and captured through calculation of a bow shape coeffi- within the Bow Intermediate ice belt area of Polar Clas- cient (fa). The hull angles are defined in Fig. 2.2.

Table 2.1 Class factors

Crushing failure Flexural failure Load patch Displacement Longitudinal Polar Class class factor class factor dimensions class class factor strength class (CFC) (CFF) factor (CFD) (CFDIS) factor (CFL) PC1 17,69 68,60 2,01 250 7,46 PC2 9,89 46,80 1,75 210 5,46 PC3 6,06 21,17 1,53 180 4,17 PC4 4,50 13,48 1,42 130 3,15 PC5 3,10 9,00 1,31 70 2,50 PC6 2,40 5,49 1,17 40 2,37 PC7 1,80 4,06 1,11 22 1,81

I - Part 1 Section 2 C Structural Requirements Chapter 22 GL 2008 Page 2–3

Note: β' = normal frame angle at upper ice waterline [°] α = upper ice waterline angle [°] γ = buttock angle at upper ice waterline (angle of buttock line measured from horizontal) [°] tan (β) = tan (α) / tan (γ) tan (β') = tan (β) cos (α)

Fig. 2.2 Definition of hull angles

2.1.2 The waterline length of the bow region is D = ship displacement [kt], not to be taken generally to be divided into 4 sub-regions of equal less than 5 kt length. The force (F), line load (Q), pressure (P) and load patch aspect ratio (AR) are to be calculated with CFC = crushing failure class factor from Table respect to the mid-length position of each sub-region 2.1 (each maximum of F, Q and P is to be used in the CFF = flexural failure class factor from Table calculation of the ice load parameters Pavg, b and w). 2.1

2.1.3 The Bow area load characteristics are deter- 2) Force F: mined as follows: 0.64 Fi = fai · CFC · D [MN] 1) Shape coefficient fai: 3) Load patch aspect ratio AR:

fai = minimum (fai,1 ; fai,2 ; fai,3) ARi = 7,46 ⋅ sin (β'i) ≥ 1,3

0,097−− 0,68 (x / L 0,15)2 4) Line load Q: fai,1 = ⋅αi β' FCF0,61 ⋅ i Q = i D [MN/m] i 0,35 AR i 1, 2⋅ CFF fai,2 = 0,64 CFD = load patch dimensions class factor from sinβ⋅ 'iC CF ⋅ D Table 2.1 fa = 0,60 i,3 5) Pressure P:

i = sub-region considered 0,22 2 0,3 Pi = Fi · CFD · ARi [MPa] L = ship length as defined in Chapter 1 – Hull Structures, Section 1, H.2.1, but 2.2 Hull areas other than the bow measured on the upper ice waterline (UIWL) [m] 2.2.1 In the hull areas other than the bow, the force (FNonBow) and line load (QNonBow) used in the determi- x = distance from the forward perpendicular nation of the load patch dimensions (bNonBow, wNonBow) (FP) to station under consideration [m] and design pressure (Pavg) are determined as follows:

α = waterline angle [°], see Fig. 2.2 1) Force FNonBow:

β'i = normal frame angle of sub-region i [°] FNonBow = 0,36 ⋅ CFC ⋅ DF [MN] Chapter 22 Section 2 C Structural Requirements I - Part 1 Page 2–4 GL 2008

DF = ship displacement factor 4. Pressure within the design load patch 0,64 = D if D ≤ CFDIS 4.1 The average pressure Pavg within a design 0,64 = CFDIS + 0,10 (D – CFDIS) load patch is to be determined as follows: if D > CFDIS F P = [MPa] D = ship displacement [kt], not to be taken avg b ⋅ w less than 10 kt

CFDIS = displacement class factor from Table 2.1 F = FBow or FNonBow as appropriate for the hull area under consideration [MN] 2) Line Load QNonBow: b = bBow or bNonBow as appropriate for the hull 0,61 QNonBow = 0,639 ⋅ FNonBow ⋅ CFD [MN/m] area under consideration [m] w = w or w as appropriate for the hull 3. Design load patch Bow NonBow area under consideration [m] 3.1 In the Bow area, and the Bow Intermediate ice belt area for ships with class notation PC6 and 4.2 Areas of higher, concentrated pressure exist PC7, the design load patch has dimensions of width within the load patch. In general, smaller areas have wBow and height bBow, defined as follows: higher local pressures. Accordingly, the peak pressure factors listed in Table 2.2 are used to account for the FBow pressure concentration on localized structural mem- wBow = [m] bers. QBow

QBow 5. Hull area factors bBow = [m] PBow 5.1 Associated with each hull area is an area FBow = maximum Fi in the Bow area [MN] factor that reflects the relative magnitude of the load expected in that area. The area factor (AF) for each QBow = maximum Qi in the Bow area [MN/m] hull area is listed in Table 2.3. PBow = maximum Pi in the Bow area [MPa] 5.2 In the event that a structural member spans 3.2 In hull areas other than those covered by 3.1, across the boundary of a hull area, the largest hull area the design load patch has dimensions of width wNonBow factor is to be used in the scantling determination of and height bNonBow, defined as follows: the member.

FNonBow w NonBow = [m] 5.3 Due to their increased manoeuvrability, ships QNonBow having propulsion arrangements with azimuthing thruster(s) or "podded" propellers are to have specially w b = NonBow [m] considered stern ice belt (Si) and stern lower (Sl) hull NonBow 3, 6 area factors.

Table 2.2 Peak pressure factors

Structural Member Peak pressure factor (PPFi)

Transversely-framed PPFp = (1,8 – s) ≥ 1,2 Plating Longitudinally-framed PPFp = (2,2 – 1,2 ⋅ s) ≥ 1.5

Frames in transverse framing With load distributing stringers PPFt = (1,6 – s) ≥ 1,0 systems With no load distributing stringers PPFt = (1,8 – s) ≥ 1,2

Load carrying stringers PPFs = 1, if Sw ≥ 0,5 ⋅ w Side and bottom longitudinals PPFs = 2,0 – 2,0 ⋅ Sw / w,

Webframes if Sw < (0,5 ⋅ w)

where: s = frame or longitudinal spacing [m] Sw = web frame spacing [m] w = ice load patch width [m]

I - Part 1 Section 2 D Structural Requirements Chapter 22 GL 2008 Page 2–5

Table 2.3 Hull area factors (AF) Polar Class Hull Area Area PC1 PC2 PC3 PC4 PC5 PC6 PC7 Bow (B) All B 1,00 1,00 1,00 1,00 1,00 1,00 1,00 1 1 Ice belt BIi 0,90 0,85 0,85 0,80 0,80 1,00 1,00 Bow intermediate Lower BI 0,70 0,65 0,65 0,60 0,55 0,55 0,50 (BI) l Bottom BIb 0,55 0,50 0,45 0,40 0,35 0,30 0,25

Ice belt Mi 0,70 0,65 0,55 0,55 0,50 0,45 0,45

Midbody (M) Lower Ml 0,50 0,45 0,40 0,35 0,30 0,25 0,25 2 2 2 2 Bottom Mb 0,30 0,30 0,25

Ice belt Si 0,75 0,70 0,65 0,60 0,50 0,40 0,35

Stern (S) Lower Sl 0,45 0,40 0,35 0,30 0,25 0,25 0,25 2 2 Bottom Sb 0,35 0,30 0,30 0,25 0,15 1 See C.1.3 2 Indicates that strengthening for ice loads is not necessary

D. Shell Plate Requirements 2 AF⋅⋅ PPFpavg P 2b⎛⎞ b 500⋅⋅ s ⋅ −⎜⎟ Rss⎝⎠ 1. The minimum shell plate thickness t is given t = eH [mm] net s by: 1 + 2⋅A t = tnet + tc [mm] t = plate thickness to resist ice loads according to In the case of obliquely framed plating (70° > Ω > 20°), net linear interpolation is to be used. C. [mm] tc = corrosion and abrasion allowance according Ω = smallest angle between the waterline and the to K.2. [mm] framing, as illustrated in Fig. 2.3 [°].

2. The thickness of shell plating to resist the s = transverse frame spacing in transversely- framed ships or longitudinal frame spacing in design ice load, tnet, depends on the orientation of the framing. longitudinally-framed ships [m] In the case of transversely-framed plating (Ω ≥ 70°), AF = hull area factor from Table 2.3 including all bottom plating, i.e. plating in hull areas BIb, Mb and Sb, the net thickness is given by: PPFp = peak pressure factor from Table 2.2

AF⋅⋅ PPFp Pavg Pavg = average patch pressure specified in C.4.1 500⋅⋅ s [MPa] ReH tnet = [mm] s 2 1 + ReH = minimum nominal upper yield point [N/mm ] 2b⋅ b = height of design load patch [m], where b ≤ (A In the case of longitudinally framed plating (Ω ≤ 20°), – s/4) in the case of transversely framed plat- when b ≥ s, the net thickness is given by: ing including all bottom plating AF⋅⋅ PPF P 500⋅⋅ s p avg A = distance between frame supports, i.e. equal to R the frame span as given in E.4., but not re- t = eH [mm] net s duced for any fitted brackets [m]. When a 1 + 2⋅A load-distributing stringer is fitted, the length A need not be taken larger than the distance In the case of longitudinally framed plating (Ω ≤ 20°), from the stringer to the most distant frame when b < s, the net thickness is given by: support. Chapter 22 Section 2 E Structural Requirements I - Part 1 Page 2–6 GL 2008

Fig. 2.3 Shell framing angle Ω

Fig. 2.4 Design span of framing member

E. Framing - General rotational restraint. Fixity is to be ensured at the support of any framing which terminates within an ice- 1. Framing members of Polar Class ships are to strengthened area. See also P.1. be designed to withstand the ice loads defined in C. 4. The design span of a framing member is to be determined on the basis of its moulded length. If 2. The term "framing member" refers to trans- brackets are fitted and configured to ensure stability in verse and longitudinal local frames, load-carrying the elastic and post-yield response regions, the design stringers and web frames in the areas of the hull ex- span may be reduced in accordance with Fig. 2.4. posed to ice pressure, see Fig. 2.1. The arrangement of load-distributing stringers is to be specially consid- 5. When calculating the section modulus and ered. In general, load-distributing stringers shall be shear area of a framing member, net thicknesses of the located at or close to mid-span of transverse frames, web, flange (if fitted) and attached shell plating are to have a web height not less than 80% of transverse be used. The shear area of a framing member may frames and have at least the same net web thickness. include that material contained over the full depth of the member, i.e. web area including portion of flange, 3. The strength of a framing member is depend- if fitted, but excluding attached shell plating. ent upon the fixity that is provided at its supports. Fixity can be assumed where framing members are 6. The actual net effective shear area Aw of a either continuous through the support or attached to a framing member is given by: supporting section with a connection bracket. In other ht⋅ ⋅ϕ sin cases, simple support is to be assumed unless the con- wn w 2 Aw = [cm ] nection can be demonstrated to provide significant 100 I - Part 1 Section 2 F Structural Requirements Chapter 22 GL 2008 Page 2–7

h = height of stiffener [mm], see Fig. 2.5 flange, the plastic neutral axis shall be located a distance zna above the attached shell plate, given by: twn = net web thickness = tw – tc [mm] 100 A+ h t−⋅ 1000 t s tw = as built web thickness [mm], see Fig. 2.5 fn w wn pn zna = [mm] 2t⋅ wn tc = corrosion deduction to be subtracted from the web and flange thickness (shall not be less and the net effective plastic section modulus Z is than t as specified in K.3.) [mm] p c given by: ϕ = smallest angle between shell plate and stiffener w ⎛⎞t web, measured at the midspan of the stiffener, pn Ztszppnna=⋅⎜⎟ + sin ϕ w see Fig. 2.5. For bulb profiles and flat bars, the ⎝⎠2 angle ϕw may be taken as 90° provided the ⎡⎤2 2 smallest angle is not less than 75°. ⎢⎥()hzwnanawnw−+ z tsin ⋅ϕ + ⎣⎦[cm3] 2000

Ahzsinbcosfn⋅−⋅ϕ−⋅ϕ⎡() fc na w w w ⎤ + ⎣ ⎦ 10

8. In the case of oblique framing arrangement (70° > Ω > 20°, where Ω is defined as given in D.2.), linear interpolation is to be used.

F. Framing - Transversely Framed Side Structures and Bottom Structures

1. The local frames in transversely-framed side Fig. 2.5 Stiffener geometry structures and in bottom structures (i.e. hull areas BIb, Mb and Sb) are to be dimensioned such that the com- 7. When the cross-sectional area of the attached bined effects of shear and bending do not exceed the plate flange (Apn) exceeds the cross-sectional area of plastic strength of the member. The plastic strength is the local frame (Afn + hw ⋅ twn/100), the actual net defined by the magnitude of midspan load that causes effective plastic section modulus Zp is given by: the development of a plastic collapse mechanism.

Atfn⋅⋅⋅+⋅ϕ pn ht w wn (thsin) pn w w 2. The actual net effective shear area of the Z =+ p frame, A , as defined in E.6., shall comply with the 20 2000 3 w [cm ] following condition: A ≥ A , where: A⋅⋅ϕ−⋅ϕ (hsinbcos) w t + fn fc w w w 10 2 100⋅⋅⋅⋅⋅ 0,5 LL s AF PPFtavg ⋅ P 2 At = [cm ] s = transverse frame spacing in transversely- 0,577⋅ R eH framed ships or longitudinal frame spacing in longitudinally-framed ships [m] LL = length of loaded portion of span = lesser of a 2 and b [m] Apn = tpn · s · 10 [cm ] a = frame span as defined in E.4. [m] tpn = fitted net shell plate thickness [mm] (shall comply with tnet as required by D.2.) b = height of design ice load patch according to C.3.1 or C.3.2, as applicable [m] hw = height of local frame web [mm], see Fig. 2.5 s = transverse frame spacing [m] Afn = net cross-sectional area of local frame flange [cm2] AF = hull area factor from Table 2.3 hfc = height of local frame measured to centre of PPFt = peak pressure factor from Table 2.2 the flange area [mm], see Fig. 2.5 Pavg = average pressure within load patch according bw = distance from mid thickness plane of local to C.4. [MPa] frame web to the centre of the flange area R = minimum nominal upper yield point [N/mm2] [mm], see Fig. 2.5 eH

When the cross-sectional area of the local frame ex- 3. The actual net effective plastic section mo- ceeds the cross-sectional area of the attached plate dulus of the plate/stiffener combination Zp, as defined Chapter 22 Section 2 G Structural Requirements I - Part 1 Page 2–8 GL 2008

in E.7., is to comply with the following condition: G. Framing - Side Longitudinals (Longitudi- Zp ≥ Zpt, where Zpt is the greater calculated on the basis nally Framed Ships) of two load conditions: a) ice load acting at the midspan of the transverse frame, and b) the ice load acting near a 1. Side longitudinals are to be dimensioned such support. The parameter A1 reflects the two conditions: that the combined effects of shear and bending do not exceed the plastic strength of the member. The plastic 3 100⋅⋅⋅⋅⋅ LL Y s AF PPFtavg ⋅ P ⋅⋅ a A 1 3 strength is defined by the magnitude of midspan load Zpt = [cm ] 4R⋅ that causes the development of a plastic collapse me- eH chanism. LL Y = 10,5−⋅ a 2. The actual net effective shear area of the frame Aw as defined in E.6., is to comply with the A1 = maximum of following condition: Aw ≥ AL, where: 1 A1A = 2 j kj⋅ 100⋅ AF⋅⋅⋅⋅⋅ PPFsavg P 0,5 b 1 a 11a1++w ⋅⎡⎤ −−2 A = [cm2] ⎢⎥1 L 22⎣⎦ 0,577⋅ R eH 1 1 − AF = hull area factor from Table 2.3 2a⋅⋅ Y A = 1 1B 0,7 PPFs = peak pressure factor from Table 2.2 0, 275+⋅ 1,44 kz P = average pressure within load patch according j = 1 for framing with one simple support outside avg to C.4. [MPa] the ice-strengthened areas = 2 for framing without any simple supports b1 = ko · b2 [m] k = 1 – 0,3 / b' a1 = At / Aw o

At = minimum shear area of transverse frame as b' = b / s given in F.2. [cm2] b = height of design ice load patch according to Aw = effective net shear area of transverse frame C.3.1 or C.3.2, as applicable [m] (calculated according to E.6.) [cm2] s = longitudinal frame spacing [m] 1 k = with A as given in E.7. w 2A⋅ fn b2 = b (1 - 0.25 · b’) [m], if b' < 2 1 + fn Aw = s [m], if b' ≥ 2 kz = zp / Zp in general, kz = 0 when the frame is a = longitudinal design span as given in E.4. [m] arranged with a bracket 2 ReH = minimum nominal upper yield point [N/mm ] zp = sum of individual plastic section moduli of flange and shell plate as fitted 3. The actual net effective plastic section 2 2 modulus of the plate/stiffener combination Z , as bt⋅ bteff⋅ pn p ffn+ defined in E.7., is to comply with the following condi- 44 3 = [cm ] tion: Z ≥ Z , where: 1000 p pL b = flange breadth [mm], see Fig. 2.5 10022⋅ AF⋅⋅⋅⋅⋅ PPF P b a A f savg1 4 3 ZpL = [cm ] tfn = net flange thickness [mm] 8R⋅ eH = tf – tc (tc as given in K.3.) 1 A4 = tf = as-built flange thickness [mm], see Fig. 2.5 2 2k+ w4⋅−() 1a − 1 tpn = the fitted net shell plate thickness [mm] (not to be less than t as given in D.2.) net a4 = AL / Aw b = effective width of shell plate flange [mm] eff AL = minimum shear area for longitudinal as given = 500 s in G.2. [cm2]

Zp = net effective plastic section modulus of trans- Aw = net effective shear area of longitudinal (cal- verse frame (calculated according to E.7.) [cm3] culated according to E.6.) [cm2]

4. The scantlings of the frame are to meet the 4. The scantlings of the longitudinals are to structural stability requirements of I. meet the structural stability requirements of I. I - Part 1 Section 2 I Structural Requirements Chapter 22 GL 2008 Page 2–9

H. Framing - Web Frame and Load-Carrying 2. Framing members for which it is not practi- Stringers cable to meet the requirements of 1. (e.g. load carrying stringers or deep web frames) shall have their webs 1. Web frames and load-carrying stringers are to effectively stiffened. The scantlings of the web stiff- be designed to withstand the ice load patch as defined eners are to ensure the structural stability of the fram- in C. The load patch is to be applied at locations ing member. The minimum net web thickness for where the capacity of these members under the com- these framing members is given by: bined effects of bending and shear is minimised. R t = 2,63⋅⋅⋅ 10−3 c eH [mm] wn 1 2 2. For web frames and load-carrying stringers, a ⎛⎞c stress analysis shall demonstrate that equivalent stres- 5,34+⋅ 4 ⎜⎟1 ses in the structure, under the combined effects of ⎝⎠c2 shear and bending, nowhere exceed the minimum nominal upper yield point ReH. Where these members c1 = hw – 0,8 ⋅ h [mm] form part of a structural grillage system, appropriate methods of analysis are to be used. Where the struc- hw = web height of stringer / web frame [mm] (see tural configuration is such that members do not form Fig. 2.6) part of a grillage system, the appropriate peak pressure h = height of framing member penetrating the factor (PPF) from Table 2.2 is to be used. member under consideration (0 if no such framing member) [mm] (see Fig. 2.6) 3. Special attention is to be paid to the shear capacity in way of lightening holes and cut-outs in c2 = spacing between supporting structure ori- way of intersecting members. ented perpendicular to the member under consideration [mm] (see Fig. 2.6) 4. The scantlings of web frames and load- carrying stringers are to meet the structural stability 3. In addition, the following is to be satisfied: requirements of I.2. R t0,35t≥⋅⋅eH wn pn 235 I. Framing - Structural Stability tpn = net thickness of the shell plate in way the 1. To prevent local buckling in the web, the framing member [mm] ratio of web height (hw) to net web thickness (twn) of any framing member shall not exceed: 4. To prevent local flange buckling of welded profiles, the following are to be satisfied: h 282 For flat bar sections: w ≤ 1) The flange width b [mm] is not to be less than twn ReH f five times the net thickness of the web twn. h 805 For bulb, tee and angle sections: w ≤ 2) The flange outstand bout [mm] is to meet the twn ReH following requirements: b 155 hw = web height out ≤ tfn ReH twn = net web thickness 2 ReH = minimum nominal upper yield point [N/mm ] bout = bf / 2 + bw – tw / 2 [mm] (see Fig. 2.5)

Fig. 2.6 Parameter definition for web stiffening Chapter 22 Section 2 L Structural Requirements I - Part 1 Page 2–10 GL 2008

J. Plated Structures L. Materials

1. Plated structures are those stiffened plate 1. Plating materials for hull structures are to be elements in contact with the hull and subject to ice not less than those given in Tables 2.6 and 2.7 based loads. These requirements are applicable to an in- on the as-built thickness of the material, the Polar board extent which is the lesser of: Class Notation assigned to the ship and the material 1) web height of adjacent parallel web frame or class of structural members given in 2. stringer; or 2. Material classes specified in Table 2.2 of Chap- 2) 2,5 times the depth of framing that intersects the ter 1 – Hull Structures, Section 2 are applicable to plated structure Polar Class ships regardless of the ship's length. In addition, material classes for weather and sea exposed 2. The thickness of the plating and the scant- structural members and for members attached to the lings of attached stiffeners are to be such that the de- weather and sea exposed plating of Polar Class ships gree of end fixity necessary for the shell framing shall are given in Table 2.5. Where the material classes in be ensured. Table 2.5 and those in Table 2.2 of Chapter 1 – Hull Structures, Section 2 differ, the higher material class is 3. The stability of the plated structure is to ade- to be applied. quately withstand the ice loads defined in C. 3. Steel grades for all plating and attached framing of hull structures and appendages situated below K. Corrosion/Abrasion Additions and Steel the level of 0,3 m below the lower waterline, as shown Renewal in Fig. 2.7, are not to be less than given in Table 2.7 of Chapter 1 – Hull Structures, Section 2, regardless of 1. Effective protection against corrosion and Polar Class. ice-induced abrasion is required for all external surfaces of the shell plating for all Polar Class ships. 4. Steel grades for all weather exposed plating of hull structures and appendages situated above the 2. The values of corrosion/abrasion additions tc level of 0,3 m below the lower ice waterline, as shown to be used in determining the shell plate thickness for in Fig. 2.7, are to be not less than given in Table 2.6. each Polar Class are listed in Table 2.4. 5. Steel grades for all inboard framing members 3. Polar Class ships shall have a minimum cor- attached to weather exposed plating are to be not less rosion/abrasion addition of tc = 1,0 mm applied to all than given in Table 2.7. This applies to all inboard internal structures within the ice-strengthened hull framing members as well as to other contiguous in- areas, including plated members adjacent to the shell, board members (e.g. bulkheads, decks) within 600 as well as stiffener webs and flanges. mm of the exposed plating.

4. Steel renewal for ice strengthened structures 6. Castings shall have specified properties con- is required when the gauged thickness is less than tnet sistent with the expected service temperature for the + 0,5 mm. cast component.

Fig. 2.7 Steel grade requirements for submerged and weather exposed shell plating

Table 2.4 Corrosion/abrasion additions for shell plating

tc [mm] Hull area With effective protection Without effective protection PC1– PC3 PC4 & PC5 PC6 & PC7 PC1– PC3 PC4 & PC5 PC6 & PC7 Bow; Bow Intermediate ice belt 3,5 2,5 2,0 7,0 5,0 4,0 Bow Intermediate Lower; 2,5 2,0 2,0 5,0 4,0 3,0 Midbody & Stern ice belt Midbody & Stern Lower; Bottom 2,0 2,0 2,0 4,0 3,0 2,5

I - Part 1 Section 2 L Structural Requirements Chapter 22 GL 2008 Page 2–11

Table 2.5 Material classes for structural members of Polar Class ships

Structural members Material Class

Shell plating within the bow and bow intermediate ice belt hull areas (B, BIi) II All weather and sea exposed SECONDARY and PRIMARY, as defined in Table 2.2 of Chapter I 1 – Hull Structures, Section 2, structural members outside 0,4 L amidships Plating materials for stem and stern frames, rudder horn, rudder, propeller nozzle, shaft brackets, II ice skeg, ice knife and other appendages subject to ice impact loads All inboard framing members attached to the weather and sea-exposed plating including any I contiguous inboard member within 600 mm of the plating Weather-exposed plating and attached framing in cargo holds of ships which by nature of their I trade have their cargo hold hatches open during cold weather operations All weather and sea exposed SPECIAL, as defined in Table 2.2 of Chapter 1 – Hull Structures, II Section 2, structural members within 0,2 L from FP

Table 2.6 Steel grades for weather exposed plating 1

Material Class I Material Class II Material Class III Thickness t [mm] PC1– 5 PC6 & 7 PC1– 5 PC6 & 7 PC1-3 PC4 & 5 PC6 & 7 MS HT MS HT MS HT MS HT MS HT MS HT MS HT t ≤ 10 B AH B AH B AH B AH E EH E EH B AH 10 < t ≤ 15 B AH B AH D DH B AH E EH E EH D DH 15 < t ≤ 20 D DH B AH D DH B AH E EH E EH D DH 20 < t ≤ 25 D DH B AH D DH B AH E EH E EH D DH 25 < t ≤ 30 D DH B AH E EH 2 D DH E EH E EH E EH 30 < t ≤ 35 D DH B AH E EH D DH E EH E EH E EH 35 < t ≤ 40 D DH D DH E EH D DH F FH E EH E EH 40 < t ≤ 45 E EH D DH E EH D DH F FH E EH E EH 45 < t ≤ 50 E EH D DH E EH D DH F FH F FH E EH

Notes 1 Includes weather-exposed plating of hull structures and appendages, as well as their outboard framing members, situated above a level of 0,3 m below the lowest ice waterline. 2 Grades D, DH are acceptable for a single strake of side shell plating not more than 1,8 m wide from 0,3 m below the lowest ice waterline.

Table 2.7 Steel grades for inboard framing members attached to weather exposed plating

Thickness t PC1– PC5 PC6 & PC7 [ mm] MS HT MS HT t ≤ 20 B AH B AH 20 < t ≤ 35 D DH B AH 35 < t ≤ 45 D DH D DH 45 < t ≤ 50 E EH D DH

Chapter 22 Section 2 M Structural Requirements I - Part 1 Page 2–12 GL 2008

M. Longitudinal Strength eb = bow shape exponent which best de- scribes the waterplane (see Figs. 2.8 and 1. Application 2.9) Ice loads need only be combined with still water loads. = 1,0 for a simple wedge bow form The combined stresses are to be compared against per- = 0,4 to 0,6 for a spoon bow form missible bending and shear stresses at different locations along the ship’s length. In addition, sufficient = 0 for a landing craft bow form local buckling strength shall also be verified. An approximate eb determined by a simple fit is acceptable. 2. Design vertical ice force at the bow γstem = stem angle to be measured between the The design vertical ice force at the bow FIB is to be horizontal axis and the stem tangent at taken as the upper ice waterline [°] (buttock angle as per Fig. 2.2 measured on the centre- FIB = minimum (FIB,1; FIB,2) [MN] line)

0,15 0,2 0,5 F = 0,534 ⋅ K ⋅ sin (γ ) ⋅ (D ⋅ K ) ⋅ CF 1 IB,1 I stem h L C = e [MN] ⎛⎞L b 2 ⋅ B ⎜⎟B FIB,2 = 1,20 ⋅ CFF [MN] ⎝⎠ B = greatest moulded breadth of the ship KI = indentation parameter = Kf / Kh [m] a) for the case of a blunt bow form LB = bow length used in the equation [m] 0,9 eb ⎛⎞2CB⋅⋅1e− b Bx⎛⎞ K = ⋅γtan( )−⋅+0,9 (1 eb ) y =⋅⎜⎟ (see Figs. 2.8 and 2.9) f ⎜⎟stem 2L ⎝⎠1e+ b ⎝⎠B D = ship displacement [kt], not to be taken b) for the case of wedge bow form (α < 80°), stem less than 10 kt eb =1 and the above simplifies to A = ship waterplane area [m2] 0,9 wp ⎛⎞ tan(αstem ) K = ⎜⎟ CFF = flexural failure class factor from Table f ⎜⎟2 ⎝⎠tan (γstem ) 2.1 Where applicable, draught dependent quantities Kh = 0,01 ⋅ Awp [MN/m] shall be determined at the waterline correspond- CFL = longitudinal strength class factor from ing to the loading condition under considera- Table 2.1 tion.

Fig. 2.8 Bow shape definition I - Part 1 Section 2 M Structural Requirements Chapter 22 GL 2008 Page 2–13

Fig. 2.9 Illustration of eb effect on the bow shape for B = 20 and LB =16

-0,2 3. Design vertical shear force MI = 0,1 ⋅ Cm ⋅ L ⋅ sin (γstem) ⋅ FIB [MNm]

3.1 The design vertical ice shear force, QI, along L = ship length as defined in Chapter 1 – Hull the hull girder is to be taken as: Structures, Section 1, H.2.1, but measured on the upper ice waterline (UIWL) [m] QI = Cf · FIB [MN] γstem = stem angle to be measured between the hori- Cf = longitudinal distribution factor to be taken as zontal axis and the stem tangent at the upper follows: ice waterline [°] (buttock angle as per Fig. 2.2 measured on the centreline) a) Positive shear force FIB = design vertical ice force at the bow [MN] Cf = 0,0 between the aft end of L and 0,6 L (calculated according to M.2.) from aft Cm = longitudinal distribution factor for design Cf = 1,0 between 0,9 L from aft and the vertical ice bending moment to be taken as forward end of L follows: b) Negative shear force Cm = 0,0 at the aft end of L

Cf = 0,0 at the aft end of L Cm = 1,0 between 0,5 L and 0,7 L from aft Cf = –0,5 between 0,2 L and 0,6 L from aft Cm = 0,3 at 0,95 L from aft C = 0,0 between 0,8 L from aft and the f C = 0,0 at the forward end of L forward end of L m Intermediate values are to be determined by Intermediate values are to be determined by linear interpolation. linear interpolation Where applicable, draught dependent quantities are to 3.2 The total vertical shear force QT for any cross be determined at the waterline corresponding to the section within the length L is to be determined by loading condition under consideration. combining the design vertical ice shear force with still water shear forces, i.e. QT = QI + QSW. 4.2 The total vertical bending moment MT for any cross section within the length L is to be deter- 4. Design vertical ice bending moment mined by combining the design vertical ice bending moment with still water bending moments MSW. The 4.1 The design vertical ice bending moment MI still water bending moment is to be taken as the along the hull girder is to be taken as: maximum sagging moment, i.e. MT = MI + MSW. Chapter 22 Section 2 P Structural Requirements I - Part 1 Page 2–14 GL 2008

5. Longitudinal strength criteria O. Appendages

5.1 Applied stresses resulting from combined ice 1. All appendages are to be designed to with- and still water loads (i.e. MT and QT) shall not exceed stand forces appropriate for the location of their at- the permissible stresses provided in Table 2.8. tachment to the hull structure or their position within a hull area. Table 2.8 Longitudinal strength criteria 2. All manoeuvring arrangements, e.g. rudder stocks, rudder couplings, rudder bearings, rudder Permissible Permissible bodies, ice horns, propeller nozzles, podded propul- Failure Applied stress when stress when mode stress sors, azimuth thrusters etc., are to be dimensioned to ReH / Rm ≤ 0,7 ReH / Rm > 0,7 withstand the design ice force defined in C.2.2.1, adjusted by the appropriate hull area factor in Table Tension σa η ⋅ ReH η ⋅ 0,41 (Rm + ReH) 2.3. Alternative design ice force definitions, including reduced design ice forces below the lower ice water- η⋅R η⋅0, 41 ⋅ (R + R ) Shear τ eH meH line (LIWL) and longitudinal design ice forces (where a 3 3 applicable), may be agreed with GL.

σc for plating and for web 3. The design ice force shall be applied at loca- σa plating of stiffeners Buckling tions where the capacity of these structural members σc/1,1 for stiffeners under the combined effects of bending, shear and τ τ torsion (where applicable) is minimised. A stress a c analysis shall demonstrate that equivalent stresses in

the structure nowhere exceed the minimum nominal upper yield point ReH. 2 σa = applied vertical bending stress [N/mm ]

τ = applied vertical shear stress [N/mm2] 4. The thickness of rudder and nozzle plating is a to be determined according to D. 2 ReH = minimum nominal upper yield point [N/mm ] 5. Rudders and rudder stocks shall be pro- R = ultimate tensile strength of material [N/mm2] m tected from ice loads with an ice horn which is fitted directly abaft the rudder and which extends a mini- σc = critical buckling stress in compression, according to Chapter 1 – Hull Structures, Sec- mum distance of 1,5 CFD [m] below the lower ice tion 3, F. [N/mm2] waterline (LIWL) defined in Section 1, C. When dimensioning the ice horn and the uppermost part of the τc = critical buckling stress in shear, according to rudder, it may be assumed that the design ice patch is Chapter 1 – Hull Structures, Section 3, F. acting over both structures, i.e. the design ice force [N/mm2] defined in 2. may be distributed between them.

η = 0,8 6. When bilge keels are fitted, it is required that they be divided into several independent lengths to limit possible damage to the shell. N. Stem and Stern Frames

1. The stem is to be shaped in such a way that it P. Local Details can break ice effectively. The thickness of the stem plating is not to be less than 1,3 times the thickness of the adjacent shell plating. 1. The intersection and termination of framing members at supporting structures, i.e. stringers, web frames, decks or bulkheads, shall be arranged to en- 2. The stern frame is to be shaped in such a way able the transfer of ice-induced loads (bending mo- that it can displace broken ice effectively. ments and shear forces), generally by means of direct welding, collar plates, lugs, connection brackets or heel stiffeners. 3. For Polar Class ships requiring E3 or E4 equivalency (see Chapter 1 – Hull Structures, Section 15, A.), the requirements of Chapter 1 – Hull Struc- 2. The loads carried by a member in way of cut- tures, Sections 15, B.5. to 15, B.7. need also to be outs shall not cause instability. Where necessary, the observed. structure is to be stiffened. I - Part 1 Section 2 R Structural Requirements Chapter 22 GL 2008 Page 2–15

Q. Direct Calculations 3. The calculations shall demonstrate that equivalent stresses in the structure, under the combined effects of shear and bending, nowhere exceed the 1. Direct calculations shall not be utilised as an minimum nominal upper yield point ReH. alternative to the analytical procedures prescribed in these Guidelines. R. Welding 2. Where direct calculations are used to check the strength of structural arrangements (e.g. arrange- 1. All welding within ice-strengthened areas is ments which may need to be specially considered), the to be of the double continuous type. load patch specified in C. shall be applied at locations where the capacity of these systems under the com- 2. Continuity of strength is to be ensured at all bined effects of bending and shear is minimized. structural connections.

I - Part 1 Section 3 B Machinery Requirements Chapter 22 GL 2008 Page 3–1

Section 3

Machinery Requirements

A. General – Detailed drawings of the main propulsion machinery. Description of the main propulsion, 1. Scope steering, emergency and essential auxiliaries are to include operational limitations. Information The contents of this Section apply to main propulsion, on essential main propulsion load control func- steering gear, emergency and auxiliary systems essential tions. for the safety of the ship and the survivability of the crew. – Description detailing how main, emergency and The vessel operating conditions are defined in Section 1. auxiliary systems are located and protected to prevent problems from freezing, ice and snow The requirements herein are additional to those appli- and evidence of their capability to operate in in- cable for the basic class. tended environmental conditions. Note – Calculations and documentation indicating compliance with the requirements of this Sec- Reference is made to Part A (Construction Provisions) tion. of the IMO Guidelines for Ships Operating in Arctic Ice-Covered Waters (MSC/Circ. 1056, MEPC/Circ. 399, 23 December 2002) for additional guidance concerning machinery arrangements. B. Materials

2. Definitions 1. Materials exposed to seawater The following main parameters are used: Materials exposed to sea water, such as propeller CP = controllable pitch propeller blades, propeller hub and cast thruster body shall have an elongation not less than 15 % on a test specimen d = propeller hub diameter [m] with a length which is five times the diameter of test D = diameter of propeller [m] specimen. EAR = expanded blade area ratio [-] Charpy V impact tests shall be carried out for materials other than bronze and austenitic steel. Average FP = fixed pitch propeller impact energy of 20 J taken from three Charpy V tests LIWL = minimum ballast waterline in ice is to be obtained at minus 10 ºC. n = rotational propeller speed [rps] 2. Materials exposed to sea water temperature N = number of loads Materials exposed to sea water temperature shall be of R = radius of the propeller [m] steel or other approved ductile material. S = safety factor [-] Average impact energy value of 20 J taken from three Charpy V tests is to be obtained at minus 10 ºC. z = number of propeller blades This requirement applies to blade bolts, CP-mecha- ϕ = propeller rotation angle [degrees] nisms, shaft bolts, strut-pod connecting bolts, etc. µ = friction coefficient [-] This does not apply to surface hardened components, such as bearings and gear teeth. 3. Documents for approval For definition of structural boundaries exposed to sea The following documents have to be submitted in trip- water temperature see Section 2, Fig. 2.7. licate or by email to the GLOBE system (http://www. gl-group.com/brochurepdf/0E088.pdf; http://www.gl- 3. Material exposed to low air temperature group.com/globe/; https://www.gl-group.com/components/index_registration.htm). Materials of essential components exposed to low air temperature shall be of steel or other approved ductile – Details of the environmental conditions and the material. An average impact energy value of 20 J required ice class for the machinery, if different taken from three Charpy V tests is to be obtained at from ship’s ice class. 10 ºC below the lowest design temperature. Chapter 22 Section 3 D Machinery Requirements I - Part 1 Page 3–2 GL 2008

This does not apply to surface hardened components, ing mode. Ice loads on bow propellers shall receive such as bearings and gear teeth. special consideration to the discretion of GL. The given loads are expected, single occurrence, maximum For definition of structural boundaries exposed to air values for the whole ships service life for normal temperature see Section 2, Fig. 2.7. operational conditions. These loads do not cover off- design operational conditions, which cannot be expected while operating the ship with good seamanship C. Design Principles knowledge as defined in Section 1, A.1. For example loads occurring when a stopped propeller is dragged 1. General through ice. These Rules cover loads due to propeller ice interaction also for azimuth and fixed thrusters All components and systems shall be designed such with geared transmission or integrated electric motor that the task of the ship in the relevant ice and weather ("geared and podded propulsors"). conditions can be fulfilled with reasonable safety. The principle of the pyramid of strength has to be followed. The loads given herein are total loads (unless otherwise stated) during ice interaction and are to be ap- 2. Ship operation in case of damage plied separately (unless otherwise stated) and are intended for component strength calculations only. Ships classed PC1 to PC5 inclusive shall have means provided to ensure sufficient ship operation in the case 2. Propeller blades of propeller damage including CP-mechanism (i.e. pitch control mechanism). Sufficient ship operation 2.1 Design ice loads means that the ship shall be able to reach safe harbour (safe location) where repair can be undertaken in case Fb is a force bending a propeller blade backwards when of propeller damage. This may be achieved either by a the propeller mills an ice block while rotating ahead. temporary repair at sea, or by towing assistance pro- Ff is a force bending a propeller blade forwards when a vided the availability can be demonstrated (condition propeller interacts with an ice block while rotating ahead. for approval, to be mentioned in Class Certificate) 2.1.1 Ice Class Factors 3. Propulsion line components The Table 3.1 lists the design ice thickness Hice and The strength of the propulsion line components shall ice strength index Sice to be used for estimation of the be designed: propeller ice loads. a) for maximum loads in D.2. (for open and ducted Table 3.1 Definition of ice strength index propellers respectively) and E.1. b) such that the plastic bending of a propeller blade Ice Class Hice [m] Sice [-] shall not cause damages in other propulsion line PC1 4,0 1,2 components PC2 3,5 1,1 c) with fatigue strength as determined in e.g. D.2.2, PC3 3,0 1,1 E.2.2 and F.1.2.3. PC4 2,5 1,1 4. Reverse operation of propellers PC5 2,0 1,1 PC6 1,75 1 Means shall be provided to free a stuck propeller by turning backwards. This means that a plant intended PC7 1,5 1 for unidirectional rotation is to be equipped at least with a sufficient turning gear that is capable of turning 2.1.2 Design ice loads for open propellers the propeller in reverse direction. 2.1.2.1 Maximum backward blade force Fb 5. Drainage When D < Dlimit: Systems, subject to damage by freezing, shall be drainable. 0,3 0,7 ⎡⎤EAR 2 [kN] (3.1) F27SnDbice= ⋅⋅⋅[] ⋅⎢⎥ ⋅ D ⎣⎦z

D. Propeller When D ≥ Dlimit:

0,3 1. General 0,7 ⎡⎤EAR 1,4 [kN] (3.2) F23SnDbice= ⋅⋅⋅⋅[]⎢⎥ ⋅⎣⎦⎡⎤ H ice ⋅ D ⎣⎦z These Rules cover open and ducted type propellers situated at the stern of a vessel having controllable 1, 4 pitch or fixed pitch blades, acting in pulling or push- Dlimit = 0,85⋅ ⎣⎡ Hice ⎦⎤ [m] (3.3) I - Part 1 Section 3 D Machinery Requirements Chapter 22 GL 2008 Page 3–3

n = nominal rotational speed (at MCR free run- 2.1.3 Design ice loads for ducted propellers ning condition) for CP-propeller and 85 % of the nominal rotational speed (at MCR free 2.1.3.1 Maximum backward blade force Fb running condition) for a FP-propeller (regard- When D < D : less driving engine type) [rps] limit 0,3 Fb is to be applied as a uniform pressure distribution 0,7 ⎡⎤EAR 2 [kN] (3.7) F9,5SnDbice= ⋅⋅⋅[] ⋅⎢⎥ ⋅ D to an area on the back (suction) side of the blade for ⎣⎦z the following load cases: When D ≥ Dlimit: a) Load case 1: from 0,6 R to the tip and from the blade leading edge to a value of 20 % of the 0,3 0,7 ⎡⎤EAR 1,4 0,6 [kN] (3.8) chord length F66SnDbice=⋅ ⋅⋅[] ⋅⎢⎥ ⋅⎣⎦⎡⎤ H ice ⋅ D ⎣⎦z b) Load case 2: a load equal to 50 % of the Fb is to be applied on the propeller tip area outside of where Dlimit = 4 ⋅ Hice 0,9 R n shall be taken as in 2.1.2.1 c) Load case 5: for reversible propellers a load Fb is to be applied as a uniform pressure distribution to equal to 60 % of the Fb is to be applied from 0,6 an area on the back (suction) side for the following R to the tip and from the blade trailing edge to a load cases: value of 0,2 chord lengths measured from trailing edge. a) Load case 1: On the back of the blade from 0,6 R to the tip and from the blade leading edge to a See description of the load cases 1, 2 and 5 in Table 1 value of 0,2 chord lengths of Annex A. b) Load case 5: For reversible rotation propellers a 2.1.2.2 Maximum forward blade force Ff load equal to 60 % of Fb is applied on the blade face from 0,6 R to the tip and from the blade When D < Dlimit: trailing edge to a value of 0,2 chord lengths measured from trailing edge ⎡⎤EAR 2 F250f =⋅⎢⎥ ⋅ D [kN] (3.4) See load cases 1 and 5 in Table 2 of Annex A. ⎣⎦z 2.1.3.2 Maximum forward blade force Ff When D ≥ Dlimit: When D < Dlimit: ⎡⎤ ⎡⎤EAR ⎢⎥1EAR⎡ ⎤ F250= ⋅⋅ D2 [kN] (3.9) F500=⋅⎢⎥ ⋅⋅ H ⋅ D [kN] (3.5) f ⎢⎥z ficed ⎢ z ⎥ ⎣⎦ ⎢⎥1− ⎣ ⎦ ⎢⎥ ⎣⎦D When D ≥ Dlimit:

⎡⎤ ⎡⎤ ⎢⎥ ⎢⎥1EAR⎡ ⎤ [kN] (3.10) 2 F500fice= ⋅⋅⋅⋅⎢⎥ H D Dlimit = ⎢⎥H [m] (3.6) d ⎢ z ⎥ d ice ⎢⎥1− ⎣ ⎦ ⎢⎥1− ⎣⎦⎢⎥D ⎣⎦⎢⎥D ⎡⎤ Ff is to be applied as a uniform pressure distribution to ⎢⎥2 where Dlimit = ⋅ H [m] (3.11) an area on the face (pressure) side of the blade for the ⎢⎥d ice ⎢⎥1 − following load cases: ⎣⎦⎢⎥D a) Load case 3: from 0,6 R to the tip and from the Ff is to be applied as a uniform pressure distribution to blade leading edge to a value of 20 % of the an area on the face (pressure) side for the following chord length load case: b) Load case 4: a load equal to 50 % of the Ff is to a) Load case 3: On the blade face from 0,6 R to be applied on the propeller tip area outside of the tip and from the blade leading edge to a 0,9 R value of 50 % of the chord length c) Load case 5: for reversible propellers a load b) Load case 5: A load equal to 60 % Ff is to be equal to 60 % Ff is to be applied from 0,6 R to the applied from 0,6 R to the tip and from the tip and from the blade trailing edge to a value of blade leading edge to a value of 0,2 chord 0,2 chord lengths measured from trailing edge. lengths measured from trailing edge See description of the load cases 3, 4 and 5 in Table 1 See description of the load cases 3 and 5 in Table 2 in of Annex A. Annex A. Chapter 22 Section 3 D Machinery Requirements I - Part 1 Page 3–4 GL 2008

2.1.4 Blade failure load for both open and n = rotational propeller speed at bollard condi- ducted propeller Fex tion. If not known, n is to be taken as defined in Table 3.2. [rps] The force Fex is acting at 0,8 R in the weakest direction of the blade at mid chord. For calculation of spindle torque the force is assumed to act at a spindle arm Table 3.2 Rotational speed at bollard condition of 2/3 of the distance from the axis of blade rotation to the leading or the trailing edge, whichever is greater, Propeller type Rotational speed n L . ex CP propellers nn The blade failure load is: FP propellers driven by turbine or electric nn 2⋅ 0,3⋅⋅ c t ⋅σref 3 motor F10ex =⋅ [kN] (3.12) 0,8⋅−⋅ D 2 r FP propellers driven by 0,85⋅ n diesel engine n

σ=ref0,6 ⋅σ+ 0,2 0, 4 ⋅σ u [MPa] (3.13) nn = nominal rotational speed at MCR, free run- where σu (specified maximum ultimate tensile ning condition [rps] strength) and σ (specified maximum yield or 0,2 % 0,2 For CP propellers, propeller pitch P shall corre- proof strength) are representative values for the blade 0,7 spond to MCR in bollard condition. If not known, P material. Representative in this respect means values 0,7 for the considered section. These values may either be is to be taken as 0,7 ⋅ P0,7n, where P0,7n is propeller obtained by means of tests, or commonly accepted pitch at MCR free running condition. "thickness correction factors" approved by GL. If not available, maximum specified values shall be used. 2.2 Dynamic analysis of blade-fatigue c, t and r are respectively the actual chord length, 2.2.1 Number of ice loads Nice thickness and radius of the cylindrical root section of the blade at the weakest section outside root fillet Number of load cycles Nice in the load spectrum per which will typically be at the termination of the fillet blade is to be determined according to the formula: into the blade profile. Nice= kk 1⋅⋅ 2 N class ⋅ n (3.16) 2.1.5 Maximum propeller ice torque applied to N = reference number of impacts per propeller ro- both, open and ducted propeller Qmax class tation speed for each ice class, acc. Table 3.3. When D < Dlimit: Table 3.3 Reference number of impacts 0,16 ⎡⎤d ⎡ P0,7 ⎤ Qkmax=⋅−⋅ open / ducted 1⎢ ⎥ Ice ⎢⎥DD PC1 PC2 PC3 PC4 PC5 PC6 PC7 ⎣⎦⎣ ⎦ [kNm] (3.14) Class

0,17 3 6 6 6 6 6 6 6 ⋅⋅[]nD ⋅ D Nclass 21 × 10 17 × 10 15 × 10 13 × 10 11 × 10 9 × 10 6 × 10

k = 1 for centre propeller kopen = 14,7 for PC1 – PC5; and 1 = 2 for wing propeller kopen = 10,9 for PC6 – PC7 = 3 for pulling propeller (wing and centre) kducted = 10,4 for PC1 – PC5; and k2 = 0,8 - f when f < 0 kducted = 7,7 for PC6 – PC7 = 0,8 – 0,4·f when 0 ≤f ≤ 1 When D ≥ Dlimit: = 0,6 – 0,2·f when 1< f ≤ 2,5

⎡⎤d 1,1 = 0,1 when f > 2,5 Q1,9k1max=⋅ open / ducted ⋅−⋅⎢⎥⎣⎡ H ice ⎦⎤ ⎣⎦D where the immersion function f is: [kNm] (3.15) 0,16 ⎡⎤P0.7 0,17 1,9 hH− ⋅⋅⋅⋅⎢⎥[]nD D f1= oice− (3.17) ⎣⎦D D/2

Dlimit = 1,8 ⋅ Hice [m] h0 = depth of the propeller centreline at the minimum ballast waterline in ice (LIWL) of the ship P0,7 = propeller pitch at 0,7 R [m] [m] I - Part 1 Section 3 D Machinery Requirements Chapter 22 GL 2008 Page 3–5

2.2.2 Distribution of ice loads ()σ=⋅σ−σice max 0,5()( ice f max () ice bmax ) (3.20) The ice load spectrum is assumed to be of the Weibull type distribution and has the general form: (σice)max = mean value of the principal stress amplitudes resulting from design forward and ⎛⎞k ⎜⎟⎛⎞F backward blade forces at the location be- ⎜⎟−⋅⎜⎟ln() N0 ⎜⎟()F 2 ⎛⎞F F ⎜⎟⎝⎠ice max ing studied. [N/mm ] Pe⎜⎟ice ≥=⎝⎠ (3.18) ⎜⎟FF ⎝⎠()icemax() ice max (σice)f max = principal stress resulting from forward 2 load Ff (2.1.2.2 and 2.1.3.2) [N/mm ] k = shape parameter of the spectrum

(σice)b max = principal stress resulting from backward N0 = number of load cycles in the spectrum 2 load Fb (2.1.2.1 and 2.1.3.1) [N/mm ] Fice = random variable for ice loads on the blade, 0 ≤ Fice ≤ (Fice)max 2.2.4 Calculation of ρ-parameter for reduction The Weibull distributions with shape parameters k = of ice load spectrum 0,75 and k = 1 are shown in Fig. 3.1. For calculation of equivalent fatigue stress two types It is suggested that the distribution with a shape pa- of S-N curves are available. rameter k = 0,75 is used for open propellers and k = 1 a) Two slope S-N curve (slopes 4.5 and 10), see for ducted propellers. Fig. 3.2. 2.2.3 Equivalent fatigue stress σ b) One slope S-N curve( the slope can be chosen), fat see Fig. 3.3. The equivalent fatigue stress for 100 million stress cycles which produces the same fatigue damage as the The type of the S-N-curve shall be selected to corre- load distribution is: spond to the material properties of the blade. If the S- N-curve is not known the two slope S-N curve shall be σ=ρ⋅σfat() ice max (3.19) used, see Fig. 3.2.

1 0 0,2 0,4 0,6 0,8 1 0,1 WeibullWeibul distributiondistribution/k=1 / k=1 WeibullWeibul distributiondistribution/k=0.75 / k=0.75 0,01

0,001

0,0001

0,00001

0,000001 Propability of exceeding for N=1E7 exceeding of Propability

0,0000001 Fice/(Ficemax) Fig. 3.1 The rainflow distribution of blade bending moment for Gudingen and Weibull distributions with shape parameters 0.75 and 1

Slope 4.5 Slope m=8

Slope 10 Slope m=10

σexp σexp Stress amplitude Stress amplitude Stress

1,E+04 1,E+06 1,E+08 1,E+10 1,E+04 1,E+06 1,E+08 1,E+10 Number of loads Number of loads Fig. 3.2 Two Slope S-N curve Fig. 3.3 Constant slope S-N curve Chapter 22 Section 3 D Machinery Requirements I - Part 1 Page 3–6 GL 2008

a) Calculation of ρ parameter for two slope S-N b) Calculation of ρ parameter for constant-slope curve S-N curve

The parameter ρ relates the maximum ice load to the For materials with a constant-slope S-N curve, see Fig distribution of ice loads according to the regression 3.3, the ρ factor shall be calculated with the following formulae: formula:

1/m CC24C3 ⎛⎞N − 1 ρ=C1icemaxfl ⋅ ( σ ) ⋅σ ⋅ log(N ice ) (3.21) ρ= Gln(N)ice k (3.23) ⎜⎟()ice ⎝⎠NR

σ=γ⋅γ⋅γ⋅σflε v m exp (3.22) where k is the shape parameter of the Weibull distribution k = 1,0 for ducted propellers and k= 0,75 for γε = reduction factor for scatter and test specimen open propellers and m is the slope of the S-N curve. size effect 8 NR = reference number of load cycles (10 ) γ = reduction factor for variable amplitude load- v m = slope parameter ing Values for the G parameter are given in Table 3.6. γm = reduction factor for mean stress Table 3.6 Value for the G parameter for differ- σexp = mean fatigue strength of the blade material at 108 cycles to failure in seawater. The follow- ent m/k ratios ing values should be used for the reduction m/k G m/k G m/k G factors if actual values are not available: γε = 2 3 6 5,5 287,9 8 40320 0,67, γv = 0,75, and γm = 0,75. [N/mm ] 3.5 11,6 6 720 8.5 119292 The coefficients C , C , C and C are given in Table 1 2 3 4 4 24 6,5 1871 9 362880 3.4. 4.5 52,3 7 5040 9.5 1,133E6 5 120 7,5 14034 10 3,623E6 Table 3.4 Definition of Calculation coefficients

Coefficients Open propeller Ducted propeller 2.3 Acceptability of blades C 1 0,000711 0,000509 2.3.1 Maximum blade stresses σcalc C2 0,0645 0,0533 Blade stresses (principal stresses) are to be calculated using the backward and forward loads, F and F re- C b f 3 -0,0565 -0,0459 spectively, given in 2.1.2 and 2.1.3 The stresses shall C4 2,22 2,584 be calculated with recognised and well documented FE-analysis or other acceptable alternative method. The calculated stresses on the blade shall not exceed the allowable stresses for the blade material given Table 3.5 Characteristic fatigue strengths for below. cast propeller materials at zero and 60 MPa mean stress. Calculated blade stress for maximum ice load shall comply with the following: Experimental σfl σfl σ < σ / S [MPa] (3.24) fatigue strength calc ref Material [MPa] [MPa] [MPa] at 1x108 cycles at zero at 60 MPa S = safety factor in sea water mean stress mean stress = 1,5 Ni Al Bronze 110 55 41 σref = reference stress, defined as the lower value of: Ni Mn Bronze 80 40 30 σref=⋅σ0,7 u or [MPa] (3.25) High tensile brass 72 36 27 σref=⋅σ+⋅σ0,6 0,2 0, 4 u [MPa] (3.26) Ferritic stainless 50 25 19 σu and σ0,2 are minimum specified values for the blade steel material according to approved maker's specification. I - Part 1 Section 3 D Machinery Requirements Chapter 22 GL 2008 Page 3–7

2.3.2 Blade tip and edge thickness t1,0 PC, tEPC 2.4 Propeller blade mounting

The blade edges and tip have to be designed such that 2.4.1 Loads during normal operation, ice contact and ice milling, no essential damage can be expected. Blade flanges and bolts are to be designed to withstand the blade failure force Fex given in 2.1.4. The blade tip thickness has to be greater than t1,0 PC given by the following formula: Separate means, e.g. dowel pins, have to be provided in order to withstand the maximum spindle torque Q (see 3.1). 500 smax t(t2D)1,0 PC=+⋅ 1,0 B [mm] (3.27) σref 2.4.2 Acceptability of bolts and pins Blade bolts shall have following minimum section The tip thickness t1,0 PC has to be measured at a dis- modulus (based on minimum diameter of shank or tance xth perpendicular to the contour edge, above thread core) around bolt pitch circle, or an other rele- 0,975 R. It needs to be demonstrated that the thickness vant axis for non circular joints, parallel to considered is smoothly interpolated between lower bound leading root section: edge thickness at 0,975 R, tip and lower bound trailing edge at 0,975 R. The basic tip thickness t has to be SF⋅⋅ (0,8D2r − ) 1,0B W10= ex bolt 6 [mm3] (3.31) chosen according to Table 3.7. bolt 2⋅σ0,2

r = radius to the bolt plan [m] Table 3.7 Basic tip thickness for propeller blades bolt S = safety factor Ice PC1 PC2 PC3 PC4 PC5 PC6 PC7 = 1,5 Class σ0,2 = minimum specified yield strength of bolt ma- t 2 1,0 B 30 28 26 24 22 19 16 terial [N/mm ] [mm] Blade bolt pre-tension shall be sufficient to avoid separation between mating surfaces with maximum xth = MIN(0,025 c0,975R; 45) [mm] (3.28) forward and backward ice loads as defined in 2.1.2 and 2.1.3 (open and ducted propeller respectively). x = distance from the blade edge [mm] th Usually 60 %-70 % of bolt yield strength is sufficient.

The blade edge thickness tEPC measured at a distance A safety factor of S = 1,5 is required to withstand the of x along the cylindrical section at any radius up to th spindle torque load Qsmax (3.1). The diameter of dowel 0,975 R has to be not less than 50 % of the tip thick- pins may be calculated by using the following formula: ness. This requirement is not applicable to the trailing edge of non reversible propellers. SQ⋅ ⋅⋅ 8 3 d10= 3 smax [mm] (3.32) 2.3.3 Acceptability criterion for fatigue PCD⋅⋅π⋅σ i 0,2

The equivalent fatigue stress at all locations on the i = number of pins blade has to fulfil the following acceptability criterion: Qsmax = according to equation 3.35. σ fl ≥1, 5 (3.29) PCD = pitch circle diameter [mm] σ fat S = safety factor = 1,5 σ=flγε ⋅ γ v⋅ γ m⋅σ exp (3.30) σ0,2 = minimum specified yield strength of bolt material [N/mm2] γε = the reduction factor for scatter and test specimen size effect 3. Pitching mechanism γv = reduction factor for variable amplitude loading 3.1 Loads due to maximum blade spindle torque Qsmax for open and ducted propellers γm = reduction factor for mean stress Spindle torque around the spindle axis of the blade σexp = mean fatigue strength of the blade material at fitting shall be calculated both for the load cases de- 8 10 cycles to failure in seawater. The follow- scribed in 2.1.3 and 2.1.4 for Fb and Ff (resulting in ing values should be used for the reduction Qsf and Qsb respectively). If these spindle torque val- factors if actual values are not available: γε = ues are less than the default value given below, the 2 0,67, γv = 0,75, and γm = 0,75. [N/mm ] default value shall be used. Chapter 22 Section 3 D Machinery Requirements I - Part 1 Page 3–8 GL 2008

The default value is: 3.4 Servo pressure

Minimum design pressure for servo system shall be taken Q0,25Fcspindle=⋅⋅ 0,7 [kNm] (3.33) as a pressure caused by Qsamax reduced by relevant friction losses in bearings caused by the respective ice loads. F is either Fb or Ff whichever has the greater absolute value. 4. Mounting of Propeller c0,7 = blade chord length at 0,7 R radius [m] Additionally the spindle torque caused by the blade 4.1 Keyless cone mounting breaking force Fex (2.1.4) has to be calculated: The friction capacity shall be at least 2,0 times the highest peak torque Qpeak as determined in E.1.1.2 2 QFL= [kNm] (3.34) without exceeding 75 % (bronze) and 80 % (steel) sex ex3 ex respectively of yield strength of the hub in terms of von Mises stress. L = maximum of distance from spindle axis to the ex The necessary surface pressure at 0 °C can be deter- leading or trailing edge at radius 0,8 R [m] mined as: The maximum spindle torque can be determined by: 22 2 2 Θ ⋅+⋅+Tf(QT)r −Θ⋅ T Qsmax = MAX (Qspindle; Qsex ; Qsf ; Qsb ) p = [MPa] (3.37) Af⋅ – Qfr1 – Qfr2 [kNm] (3.35) 2 Qsf and Qsb are the spindle torques due to the blade ⎛ μ o ⎞ 2 f = ⎜ ⎟ − Θ (3.38) forward and backward acting ice load, Ff and Fb re- ⎝ S ⎠ spectively, as given in the load cases 2.1.2 and 2.1.3. Θ = half conicity of the shaft [-] Qfr1 = friction torque in blade bearings caused by reaction forces due to Fex [kNm] Tr = propeller response thrust [kN]

Qfr2 = friction between connected surfaces resulting Q = Qpeak according to E.1.1.2 [kNm] from blade bolt pretension forces [kNm] A = effective contact area of the shrink fit [mm2] In calculating Q a friction coefficient = 0,15 may fr µ = 0,15 for steel-steel, normally be applied. 0 = 0,13 for steel-bronze 3.2 Dynamic loads for fatigue analysis Q samax S = 2,0 Fatigue strength is to be considered for parts transmit- ting the spindle torque from blades to a servo system The backward response thrust Tr for pushing propel- considering ice spindle torque acting on one blade. lers and the forward response thrust for pulling propel- The maximum amplitude is defined as: lers respectively has to be inserted and a negative sign shall be used.

QQsb+ sf Qsamax = [kNm] (3.36) 4.2 Key mounting 2 Key mounting is not permitted. Qsf and Qsb see 3.1 4.3 Flange mounting 3.3 Acceptability of pitching mechanism a) The flange thickness is to be at least 25 % of the Static calculations have to demonstrate that the com- shaft diameter. ponents of CP mechanisms are to be designed to with- b) Any additional stress raisers such as recesses for stand the blade failure spindle torque Q and maxi- sex bolt heads shall not interfere with the flange fillet. mum spindle torque Qsmax. c) The flange fillet radius is to be at least 10 % of The maximum spindle torque Q shall not lead to smax the shaft diameter. any consequential damages. d) The diameter of ream fitted (light press fit) bolts Provided that calculated stresses duly considering shall be chosen so that the peak torque Q (see local stress concentrations are less than yield strength, peak E.1.1.2) does not cause shear stresses beyond or maximum 70 % of σu of respective materials, de- 30 % of the yield strength of the bolts. tailed fatigue analysis is not required. In opposite case components shall be analysed for cumulative fatigue, e) The bolts are to be designed so that the blade based on a maximum loading by Qsamax (see 3.2). failure load Fex (see 2.1.4) in any direction (for- Similar approach as used for shafting (see E.2.2) may ward or backwards) does not cause yielding or be applied. flange opening. I - Part 1 Section 3 E Machinery Requirements Chapter 22 GL 2008 Page 3–9

E. Shafting

1. Design loads

1.1 Torque

] - 1.1.1 Torque due to a single blade impact Q(ϕ) [ ue The propeller ice torque excitation for shaft line dy- q

namic analysis shall be described by a sequence of tor act p blade impacts which are of half sine shape and occur at the blade. The torque due to a single blade ice impact as im Ice a function of the propeller rotation angle is then:

Q(ϕ= ) Cqmax ⋅ Q ⋅ sin( ϕ (180 / α i )) [kNm] (3.40) when ϕ rotates from 0 to αi plus integer revolutions.

Qmax see D.2.1.5 Time (sec) Case 1 Q(ϕ= ) 0 (3.41) when ϕ rotates from αi to 360 plus integer revolutions. φ is the rotation angle starting when the first impact occurs. Cq and αi parameters are given in Table 3.8

The total ice torque is obtained by summing the torque ] - of "individual" (single) blades taking into account the [ ue phase shift 360 degrees/z. The number of propeller q

revolutions nQ during a milling sequence shall be ob- tor act tained with the formula: p Ice im Ice n2HQice=⋅ (3.42) and total number of impacts during one ice milling sequence is z ⋅ nQ.

Table 3.8 Parameters for torque excitation Time (sec) α Case 2 Torque Propeller-ice C i excitation interaction q [degrees] Case 1 Single ice block 0,75 90 Case 2 Single ice block 1,0 135 Two ice blocks with 45 degree

Case 3 0,5 45 ] -

phase in rotation [

angle ue q

act tor act

In addition, the impacts are to ramp up over 270 de- p grees and subsequently ramp down over 270 degrees. Ice im Ice The total excitation torque from the three cases will then look like Fig. 3.4. Milling torque sequence duration and number of loads is not valid for pulling bow propellers, which are subject to special consideration. The response torque at any component in the propul- Time (sec) sion system shall be analysed considering the above Case 3 excitation torque at the propeller, the actual engine torque Qe, and the mass elastic system. Fig. 3.4 Total excitation torque Chapter 22 Section 3 E Machinery Requirements I - Part 1 Page 3–10 GL 2008

1.1.2 Response torque in the propulsion system Table 3.9 Parameters for torsional vibration Qr (t) and its maximum Qpeak calculation

1.1.2.1 The maximum torque Q may be calcu- Excitation peak No. of case (acc. f f f lated using one of the following three different ap- blades I II static proaches (a – c). With increasing simplification of Fig. 3.4) method, the result Qpeak becomes higher. 1 0,40 0 0,36 3 2 0,32 0,05 0,72 a) Transient torsional vibration analysis 3 0 0,27 0,24 The response torque at any component in the propulsion system shall be analysed considering the above 1 0,32 0,06 0,48 excitation torque at the propeller, the actual engine 4 2 0 0,05 0,95 torque Q , and the mass elastic system. See Fig. 3.5. e 3 0 0,21 0,32 The response torque Qr(t) in all components shall be 1 0,16 0 0,60 determined by means of transient torsional vibration 5 2 0,17 0 1,20 analysis of the propulsion line. Calculations have to be carried out for all excitation cases given above (1.1.1) 3 0 0,10 0,40 and the response has to be applied on top of the mean 1 0 0,04 0,72 hydrodynamic torque in bollard condition at considered propeller rotational speed. 6 2 0,10 0 1,43 3 0 0 0,48 Q (t) = Q (ϕ) + Q [kNm] (3.43) r e 1 0,10 0 0,84 7 2 0,05 0,02 1,67 b) Steady state torsional vibration calculation 3 0 0,07 0,56 The response torque Qr at any component of the propulsion system can be calculated by a steady state All values as fraction of Qmax (for use in TVC fI and fII are to be multiplied by the ratio of Q /Q ). torsional vibration calculation (TVC) considering the max nom ice excitation in 1.1.1 by using excitation factors fI st nd Qmax = propeller ice torque according to D.2.1.5 [kNm] and fII for the 1 and 2 propeller order as well as with a factor fstatic for a static part on the basis of Qnom = nominal engine torque at maximum continu- Table 3.9. ous rating (MCR) [kNm]

Qpeak 2QAmax

Fig. 3.5 Definition of torque I - Part 1 Section 3 E Machinery Requirements Chapter 22 GL 2008 Page 3–11

The response torque Qr for every single speed within – The highest torque amplitude during a sequence the operating range for each ice excitation case (Fig. of impacts is to be determined as half of the 3.4) shall be calculated according to range from maximum to minimum torque and is referred to as QAmax (see Fig. 3.5). Qr = Qe + Qstatic + Qdyn [kNm] (3.44) 1.2 Thrust Qe = actual mean torque at considered speed [kNm] 1.2.1 Maximum propeller ice thrust applied to the shaft Qstatic = fstatic ⋅ Qmax [kNm]

= static part of ice excitation torque according T1,1Fff= ⋅ [kN] (3.47) to Table 3.9 Q = result of TVC for alternating torque by using dyn T1,1Fb = ⋅ b [kN] (3.48) propeller excitation factors fI and fII acc. to Table 3.9 [kNm] For Ff, Fb see D.2.1.2 and D.2.1.3. The highest peak torque Qpeak is equal to the highest 1.2.2 Maximum response thrust T response torque Qr calculated over all excitation cases r (see 1.1.1) within the operating range. Maximum thrust along the propeller shaft line is to be calculated with the formulae below. The factors 2,2 c) Simple formula and 1,5 take into account the dynamic magnification If it can be demonstrated that no resonance of first or due to axial vibration. Alternatively the propeller second blade order against any elastic element such as thrust magnification factor may be calculated by dy- main and generator couplings (PTO) occur over the namic analysis. whole operating speed range, the highest peak torque Maximum forward shaft thrust: in the propeller shaft Qpeak can be calculated by using the following formula: Tr = T + 2,2 ⋅ Tf [kN] (3.49) Qpeak = 1,4 (Qmax + Qnom) [kNm] (3.45) Maximum astern shaft thrust: or alternatively, if Qmax cannot be determined due to lack of propeller geometry information: Tr = 1,5 ⋅ Tb [kN] (3.50)

Qpeak = 3 ⋅ Qnom [kNm] (3.46) T = propeller bollard thrust [kN]

For gear equipped propulsion systems the maximum Tf = maximum forward propeller ice thrust [kN] torque for components on input side of the gear Qpeak in shall be calculated with the following formula based Tb = maximum backward propeller ice thrust [kN] on the maximum torque Qpeak according to equations If hydrodynamic bollard thrust T is not known, T is to (3.45) respectively (3.46): be taken according to Table 3.10.

1, 3⋅ I H Qpeak in = ⋅ Qpeak [kNm] (3.46a) 1 Table 3.10 Propeller bollard thrust IIHI⋅+ u2 Propeller type T IH = moment of inertia for masses with engine speed [kgm2] CP propellers (open) 1,25 Tn II = moment of inertia for masses with propeller speed [kgm2] CP propellers (ducted) 1,1 Tn u = reduction ratio (engine speed / propeller speed) [-] FP propellers driven by turbine T or electric motor n For all components on output side of the gear Qpeak applies. FP propellers driven by diesel 0,85 T engine (open) n 1.1.2.2 The results of the three excitation cases are to FP propellers driven by diesel be used in the following way for Q and Q : 0,75 T peak Amax engine (ducted) n – The highest peak torque (between the various lumped masses in the system) is in the following Tn = nominal propeller thrust at MCR at free run- referred to as peak torque Qpeak. ning open water conditions Chapter 22 Section 3 E Machinery Requirements I - Part 1 Page 3–12 GL 2008

2. Dimensioning and acceptability strength (in order to avoid stress-strain hysteresis loop) with a safety factor of 1,25, i.e.: 2.1 Propeller shaft 2⋅σy The propeller shaft is to be designed to fulfil the fol- Δτ⋅αt ≤ [MPa] (3.54) lowing: 31,25⋅

The blade failure load Fex (see D.2.1.4) applied on the where αt is the local stress concentration factor in propeller blade at 0,8 R radius parallel to the shaft (for- torsion. ward or backwards) shall not cause yielding. The bending moment need not to be combined with any other load. 2.3 Shaft connections

This requires a minimum diameter dp in way of the aft 2.3.1 Shrink fit couplings (keyless) stern tube bearing of: The friction capacity shall be at least 1,8 times the FDex ⋅ highest peak torque Q as determined in 1.1.2 with- d160=⋅3 [mm] (3.51) peak p out exceeding 80 % of yield strength (steel). σy The necessary surface pressure can be determined σy = minimum specified yield or 0,2 % proof according to equation 3.37. strength of the propeller shaft material [MPa] In front of the aft stern tube bearing the diameter may 2.3.2 Key mounting be reduced based on the assumption that the bending Key mounting is not permitted. moment is linearly reduced to 20 % at the next bearing and in front of this linearly to zero at third bearing. 2.3.3 Flange mounting

Bending due to maximum blade forces Fb and Ff The following requirements have to be considered: (D.2.1.2 and D.2.1.3) has been disregarded, because the resulting stress levels are much below the stresses a) Any additional stress raisers such as recesses for bolt heads shall not interfere with the flange fillet due to the blade failure load Fex. b) The diameter of ream fitted (light press fit) bolts 2.2 Propeller and intermediate shafts or pins shall be chosen so that the peak torque Qpeak (see 1.1.2) does not cause shear stresses be- 2.2.1 The stresses due to the peak torque Qpeak yond 30 % of the yield strength of the bolts or pins. (1.1.2) shall have a minimum safety factor of 1,25 against yielding in plain sections and 1,0 in way of c) The bolts are to be designed so that the blade stress concentrations in order to avoid bent shafts. failure load Fex (see D.2.1.4) in backward direction does not cause yielding or flange mating The minimum diameter is: surface separation. Depending on flange posi- Plain shaft: tion, a reduction of bending load according to 2.1. is permitted. Qpeak d225p =⋅3 [mm] (3.52) 2.4 Bearings σy 2.4.1 General Notched shaft: All shaft bearings are to be designed to withstand the pro- Qpeak⋅α t peller blade ice interaction loads according to D.2. For the d=⋅ 210 3 [mm] (3.53) p σy purpose of calculation, the shafts are assumed to rotate at rated speed. Reaction forces due to the response torque Q (ϕ) (e.g. in gear transmissions) are to be considered. where αt is the local stress concentration factor in r torsion. Additionally the aft stern tube bearing as well as the next shaft line bearings are to withstand a bending 2.2.2 The torque amplitudes, based on Qpeak, with moment caused by Fex as given in D.2.1.4, in such a the foreseen number of cycles, as defined in F.1.2.3, way that the ship can maintain operational capability. shall be used in an accumulated fatigue evaluation The pressures in these bearings are to be assessed based where the safety factor is 1,5 compared with the 50 % on the bending moment distribution given in 2.1. survival probability curve. If the plant also has high engine excited torsional vibrations (e.g. direct coupled For low operational propeller speeds (e.g. for drives 2-stroke engines), this has also to be considered. with electric motors or for drives with several motors/propellers and some of the propellers part-time in 2.2.3 For plants with reversing direction of rotation "wind milling") suitable measures for maintaining the stress range Δτ ⋅ αt resulting from forward Qpeakforward bearing lubrication (e.g. additional hydrostatic lubrica- to astern Qpeakastern shall not exceed twice the yield tion) are to be provided. I - Part 1 Section 3 F Machinery Requirements Chapter 22 GL 2008 Page 3–13

2.4.2 Thrust bearings It is recommended to use "BECAL" or equivalent methods for the assessment of bevel gears. The use of Thrust bearings and their housings are to be designed to ISO 10300 is only accepted within the given limita- withstand maximum response thrust Tr according to tions of the ratio face width/module. 1.2.2 and the force resulting from the blade failure load Fex in D.2.1.4. For the purpose of calculation, except 1.2.2 Load distribution factors for Fex, the shafts are assumed to rotate at rated speed. Common for all criteria is the influence of load distri- 2.4.3 Roller bearings bution over the face width. All relevant parameters are to be considered, such as elastic deflections (of mesh, Roller bearings are to have a L lifetime of at least 10h shafts and gear bodies), accuracy tolerances, helix 40000 hours. The calculation of lifetime is to be based modifications and working positions in bearings (es- on reaction forces from the torque spectrum and prin- pecially for twin input single output gears). ciples given in F.1.2.3. 1.2.3 Contact stress 2.5 Seals The safety against pitting shall be assessed against the Seals are to be provided to prevent egress of pollutants given load spectrum as well as the ordinary loads (open and shall be suitable for the operating temperatures. water running) by means of accumulated fatigue analy- Contingency plans for preventing the egress of pollut- ses (stated in ISO 6336 Pt 6) with a minimum resulting ants under failure conditions are to be documented. safety factor SH of 1,2 (ref. ISO 6336 Pt 1, 2 and 6). Seals are to be of proven design. The ice load spectrum for the output gear is defined as:

100 % of Q peak g with nQ cycles F. Gears, Flexible Couplings, Clutches 0,2 80 % of Q peak g with (z Nice) nQ cycles 1. Gear transmissions 0,4 60 % of Q peak g with (z Nice) nQ cycles

0,6 1.1 Calculation of maximum torque Qpeak g 40 % of Q peak g with (z Nice) nQ cycles

0,8 For gear equipped propulsion systems it has to be 20 % of Q peak g with (z Nice) nQ cycles (nQ = 2 Hice) demonstrated that the gear transmission withstands n = see formula 3.42 loads based on the maximum torque Qpeakg. The ma- Q ximum torque can be calculated with the following For pinions and wheels with higher speed the numbers formula: of load cycles nQ are found by multiplication with the gear ratios. 1, 3⋅⋅ I u 2 Q = H ⋅ Q [kNm] (3.55) peak g 2 peak IuHL⋅+ I 1.2.4 Tooth root stress Tooth root safety shall be assessed in the same way as Qpeak g = maximum torque in gear mesh side [kNm] for contact stress but with a minimum safety factor SF IH = moment of inertia for masses with higher of 1,5 (ref. ISO 6336 Pt 1, 3 and 6). speed [kgm2] 1.2.5 Scuffing IL = moment of inertia for masses with lower speed [kgm2] The scuffing safety (flash temperature method according to DIN 3990, Part 4) based on the peak torque u = reduction ratio (input speed / output speed) Qpeak g shall be at least 1,2 when the FZG class of the

Qpeak = see E.1.1.2 oil is assumed one stage below specification.

1.2 Calculation of the load-bearing capacity of 1.2.6 Flank subsurface fatigue cylindrical and bevel gearing Sub-surface fatigue is mainly influenced by material microstructure, surface hardness and hardness depth. 1.2.1 General Up to now there is no standardized calculation proce- The sufficient load capacity of the gear-tooth system dure available. Therefore a careful review of each is to be demonstrated by load capacity calculations parameter concerning subsurface fatigue is necessary. while maintaining the required safety margins for the For case carburized gears the case depth should be criteria stated below. Cylindrical gears can be assessed within the recommended range stated in ISO 6336-5 on the basis of the international standard ISO 6336 clause 5.6.2/c. It should be noted that high overloads Pt. 1–6, provided that "methods B" are used. Other can initiate subsurface fatigue cracks that may lead to calculation methods may be accepted provided that a premature failure. In lieu of reliable analyses UT they are reasonably equivalent. inspection intervals may be used. Chapter 22 Section 3 G Machinery Requirements I - Part 1 Page 3–14 GL 2008

1.3 Shafts There shall be a separation margin of at least 20 % between the peak torque Qpeak and the torque where Shafts in gear transmissions shall meet the same safety any twist limitation is reached. level as intermediate shafts, but where relevant, bending stresses and torsional stresses shall be combined (e.g. by von Mises). 3. Clutches Clutches shall have a static friction torque of at least 1.4 Bearings 1,3 times the peak torque Qpeak and a dynamic friction torque of 2/3 of the static one. See E.2.4. Emergency operation of the clutch after failure, e.g. loss of operating pressure, shall be established within a 2. Flexible couplings reasonably short time. If this is arranged by bolts, they Couplings shall be designed such that frequent occur- shall be situated on the engine side of the clutch in order to ensure access to all bolts by turning the engine. rence of peak torques Qpeak (E.1.1.2) will not lead to fatigue cracking, i.e. exceeding the permissible vibra- tory torques TKmax1 or ΔTmax of the coupling. The permissible torque may be determined by interpolation G. Azimuth Propulsors in a log-log torque-cycle diagram where TKmax1 respectively ΔTKmax refers to 50000 cycles, see illustration in Fig. 3.6 and 3.7. 1. General In addition to the requirements for single components special consideration shall be given to the loading cases which are extraordinary for azimuthing propul- TKmaxl sion units when compared with conventional propulsion systems. Estimation of the load cases shall reflect the way of operation of the ship and the thrusters. In this respect, for example, the loads caused by impacts of ice blocks on the propeller hub of a pulling propeller are to be considered. Also loads due to thrusters operating in an oblique angle to the flow are to be considered.

2. Design ice loads Azimuth propulsors shall be designed for the following loads. As far as appropriate, the loads have to be applied simultaneously.

2.1 Ice pressure on strut based on defined location

Fig. 3.6 Definition of torque amplitude TKmax1 area of the strut / ice interaction as per Section 2, O.2. 2.2 Ice pressure on pod based on defined location area of thruster body / ice interaction as per Section 2, O.2. ΔTKmax

2.3 Plastic bending of one propeller blade Fex (see D.2.1.4) in the worst position (typically top- down) or maximum response thrust Tr (see E.1.2.2).

2.4 Steering gear design torque QSG shall be at least 60 % of steering torque expected at propeller ice milling condition defined as Qmax (see D.2.1.5):

Q Q = 0, 6 max ⋅ A [kNm] (3.39) SG 0,8⋅ R

A = distance from the propeller plane to steering (azimuth) axis [m]

2.5 Steering gear shall be protected by effective Fig. 3.7 Definition of torque amplitude ΔTKmax means limiting excessive torque caused by: I - Part 1 Section 3 I Machinery Requirements Chapter 22 GL 2008 Page 3–15

a) Ice milling torque exceeding design torque and I. Auxiliary Systems leading to rotation of unit. b) Torque caused by plastic bending of one propel- 1. General ler blade in the worse position (related to steer- In addition to the requirements for ice class E4 (see ing gear) and leading to rotation of the unit. Chapter 2 – Machinery Installations, Section 11) the Steering gear shall be ready for operation after above following shall be observed. loads a) or b) have disappeared. 1.1 Machinery shall be protected from the harm- ful effects of ingestion or accumulation of ice or snow. 3. Acceptability of azimuth thrusters Where continuous operation is necessary, means shall It has to be demonstrated that the individual compo- be provided to purge the system of accumulated ice or nents can withstand the loads given in 2. and in its snow. respective section with a safety factor as required for the individual component. 1.2 Suitable material for low temperatures shall be used for the pipes, valves and fittings which are The housing has to have a safety of 1,0 with respect to exposed to sea water or cold air. yield. For bolted connections the same safety factor as for 1.3 Vent pipes, intake and discharge pipes and the housing itself has to be demonstrated. However, associated systems shall be designed to prevent block- opening of the mating surfaces is not permitted. age due to freezing or ice and snow accumulation.

Slewing bearings of roller type are to have a L10h 1.4 Means shall be provided to prevent freezing lifetime of at least 40000 hours. The calculation of or salification of pipes where necessary, e.g. by trace lifetime is to be based on reaction forces from the heating. thrust spectrum given in 2. 1.5 Systems subject to freezing shall be drainable. A safety of S = 2,5 against static loads given in 2. has to be demonstrated. 1.6 Additional heating of lube oil may be needed for equipment located in machinery spaces.

H. Prime Movers 1.7 Transverse thrusters (not used for propulsion) shall be designed to avoid self destruction in case 1. Propulsion engines propeller is blocked by ice.

1.1 General 2. Sea inlets and cooling water systems

Engines are to be capable of being started and running 2.1 Cooling water systems for machinery that are the propeller in bollard condition. essential for the propulsion and safety of the ship, Propulsion plants with CP propeller are to be capable including sea chest inlets, shall be designed for the being operated even in case with the CP system in full environmental conditions applicable to the ice class. pitch as limited by mechanical stoppers. 2.2 At least two sea chests are to be arranged as 1.2 Crankshafts ice boxes (sea chests for water intake in severe ice conditions) for class PC1 to PC5 inclusive. The calcu- Special considerations apply for plants with large lated volume for each of the ice boxes shall be at least inertia (e.g. flywheel, tuning wheel or PTO) in the 1m3 for every 750 kW of the totally installed power. front of the engine (opposite to main power take off). For PC6 and PC7 there shall be at least one ice box located preferably near centre line. 2. Emergency power units 2.3 Ice boxes are to be designed for an effective Provisions shall be made for heating arrangements to ensure ready starting of the cold emergency power separation of ice and venting of air. units at expected low ambient temperature. 2.4 Sea inlet valves are to be secured directly to Emergency power units shall be equipped with starting the ice boxes. The valve shall be a full bore type. devices with a stored energy capability of at least three consecutive starts at the above mentioned temperature. 2.5 Ice boxes and sea bays are to have vent pipes The source of stored energy shall be protected to pre- and are to have shut off valves connected directly to clude critical depletion by the automatic starting sys- the shell. tem, unless a second independent mean of starting is provided. A second source of energy shall be provided 2.6 Means are to be provided to prevent freezing for an additional three starts within 30 min., unless of sea bays, ice boxes, ship side valves and fittings manual starting can be demonstrated to be effective. above the load water line. Chapter 22 Section 3 I Machinery Requirements I - Part 1 Page 3–16 GL 2008

2.7 Efficient means are to be provided to re- 5.2 The effective holding torque of the rudder circulate cooling seawater to the ice boxes. Total sec- actuator, at safety valve set pressure, is obtained by tional area of the circulating pipes is not to be less multiplying the open water requirement at design than the area of the cooling water discharge pipe. speed (maximum18 knots) by the factors defined in Table 3.11., but not less than the working torque ac- 2.8 Detachable gratings or manholes are to be cording to Chapter 2 – Machinery Installations, Sec- provided for ice boxes. Manholes are to be located tion 14, A.4.1. above the deepest load line. Access is to be provided to the ice box from above. Access hatches may be Table 3.11 Factor for holding torque of rudder used instead of manholes. actuator 2.9 Openings in ship sides for ice boxes are to be Ice fitted with gratings, or holes or slots in shell plates. PC1 PC2 PC3 PC4 PC5 PC6 PC7 The net area through these openings is to be not less Class than 5 times the area of the inlet pipe. The diameter of Factor 5 5 3 3 3 2 1,5 holes and width of slot in shell plating is to be not less than 20 mm. Gratings of the ice boxes are to be pro- The design pressure for calculating the scantlings of vided with means of clearing. Clearing pipes are to be piping and other steering gear components subjected provided with screw-down type non return valves. to internal hydraulic pressure shall be at least 1,25 times the set pressure of the safety valves, but not less 3. Ballast and other tanks than the design pressure according Chapter 2 – Ma- chinery Installations, Section 14, A.4.1. 3.1 Efficient means are to be provided to prevent freezing in fore and aft peak tanks, wing tanks, ballast 5.3 It is considered for a Polar Class ship to be tanks located above the water line and any other tanks able to move her rudder somewhat faster than a seago- where found necessary. ing ship operating in open water. So the requirements according to Chapter 2 – Machinery Installations, 3.2 Fresh water, ballast, fuel & lube oil tanks shall Section 14, A.3.2 shall be extended to a turning speed be carefully located and fitted with heating facilities. according to Table 3.12.

3.3 Heating facilities may be needed also for The minimum discharge capacity of the relief valve(s) further tanks (e.g. tanks for sludge, leakage, bilge as mentioned under 5.2 shall be determined by the water, sewage, etc.), pending on location and media. turning speed of the rudder actuator according to Ta- ble 3.12. 4. Ventilation system Table 3.12 Turning speeds for rudder actuator 4.1 The air intakes for machinery and accommodation ventilation are to be located on both sides of the Ice Class PC1–2 PC3–5 PC6–7 ship. Turning speeds 8 6 4 The air intakes are to be sufficient for safe operation [deg/s]

of the ship in heavy weather respectively in ice storm conditions. 5.4 The minimum discharge capacity of the additional relief valve(s) as mentioned under 5.3 shall be 4.2 Accommodation and ventilation air intakes determined by the turning speed for the rudder actua- shall be provided with means of heating. tor according to Table 3.13. 4.3 The temperature of combustion air is to be suitable for the operation of the machinery. Direct Table 3.13 Turning speeds of the rudder actuator ducting to the engines with own heating facilities shall for rudders pushed rapidly hard over be considered. Ice Class PC1–2 PC3–5 PC6–7 5. Steering systems Turning speeds 40 20 10 [deg/s] 5.1 Rudder stops are to be provided and integrated into the hull. The design ice force on rudder shall be transmitted to the rudder stops without dam- The fast acting relieve system shall not allow to cause age to the steering system. more than 50 % increase of torque above the set pressure of relief valves according to 5.2 due to a too Ice horn shall in general be fitted to protect the rudder slowly acting torque release system. In some cases, a in centre position. Design shall be performed accord- fast acting relief valve with typically 10 milliseconds ing to Section 2, O. response time, or a bursting disc, will be needed. I - Part 1 Section 3 K Machinery Requirements Chapter 22 GL 2008 Page 3–17

Furthermore, if the specified angular velocity results 3. Vertical impact acceleration av in an increase in torque of greater than 50 % due to constriction of hydraulic flow, means shall be pro- Combined vertical impact acceleration at any point vided to allow for an improved flow. In some cases a along the hull girder: dump tank for the hydraulic fluid may be required. FIB 2 a2,5vX= ⋅⋅ F [m/s ] (3.56) Following any event, the system capability shall be Δ regained quickly. FX = 1,3 at FP = 0,2 at midships = 0,4 at AP J. Foundation of Equipment = 1,3 at AP for vessels conducting ice breaking astern 1. General Intermediate values to be interpolated linearly. Essential equipment and supports shall be suitable for the accelerations indicated as follows. Accelerations 4. Transverse impact acceleration a are to be considered acting independently. t Combined transverse impact acceleration at any point along hull girder: 2. Longitudinal impact accelerations a1 FX 2 Maximum longitudinal impact acceleration at any a3Fti= [m/s ] (3.57) Δ point along the hull girder:

Fi = total force normal to shell plating in the bow ⎧⎫⎡ ⎤ area due to oblique ice impact, defined in FzIB⎪⎪ f 2 al =⋅⎨⎬⎡⎤ 1,1 ⋅γ+φ+⋅ tan()⎢ 7 ⎥ [m/s ] (3.55) Section 2, C.2.1.3 Δ ⎣⎦L ⎩⎭⎪⎪⎣⎢ pp ⎦⎥ FX = 1,50 at FP

FIB = vertical impact force, defined in Section 2, = 0,25 at midships M.2. = 0,50 at AP Δ = displacement of the ship [kt] = 1,50 at AP for vessels conducting ice breaking astern γ = bow stem angle at waterline [degrees] Intermediate values to be interpolated linearly. Φ = maximum friction angle between steel and ice, normally taken as 10 [degrees] K. Alternative Design zf = distance from the water line to the point being considered [m] As an alternative, a comprehensive design study may be submitted and may be requested to be validated by Lpp = length of ship between perpendiculars [m] an agreed test programme.

I - Part 1 Annex A Load Cases for Open and Ducted Propellers Chapter 22 GL 2008 Page A–1

Annex A

Load Cases for Open and Ducted Propellers

Table A.1 Load cases for open propellers

Right handed propeller blade Force Loaded area seen from back

Load case 1 Fb Uniform pressure applied on the back of the blade(suction side) to an area from 0.6R to the tip and from the leading edge to 0,2 times the chord length

Load case 2 50 % of Fb Uniform pressure applied on the back of the blade (suction side) on the propeller tip area outside of 0,9R radius.

Load case 3 Ff Uniform pressure applied on the blade face (pressure side) to an area from 0,6R to the tip and from the leading edge to 0,2 times the chord length.

Load case 4 50 % of Ff Uniform pressure applied on propeller face (pressure side) on the propeller tip area outside of 0,9R radius.

Load case 5 60 % of Ff or Fb Uniform pressure applied on propeller which one is face (pressure side) to an area from 0,6R greater to the tip and from the trailing edge to 0,2 times the chord length

Chapter 22 Annex A Load Cases for Open and Ducted Propellers I - Part 1 Page A–2 GL 2008

Table A.2 Load cases for ducted propellers

Right handed propeller blade Force Loaded area seen from back

Load case 1 Fb Uniform pressure applied on the back of the blade (suction side) to an area from 0,6R to the tip and from the leading edge to 0,2 times the chord length

Load case 3 Ff Uniform pressure applied on the blade face (pressure side) to an area from 0,6R to the tip and from the leading edge to 0,5 times the chord length.

Load case 5 60 % of Ff or Fb Uniform pressure applied on propeller which one is face (pressure side) to an area from 0,6R greater to the tip and from the trailing edge to 0,2 times the chord length

I - Part 1 Annex B C Quality Requirements for FEM Analysis Chapter 22 GL 2008 Page B–1

Annex B

Quality Requirements for FEM Analysis

A. Requirements for FE Model may also be used, however, would require a high per- formance hardware. Linear tetrahedra shall not be The objective of the stress analysis of ice-strengthened used in stress analysis. propeller blades is to make sure that the designed propeller blade has an acceptable margin of safety in Near the root region of the blade, where the geometry terms of both ultimate and fatigue strength against the changes rapidly, the used element size should be cho- design loads. sen such that the local stress concentration and stress distribution in thickness direction is reflected properly, The typical locations on the propeller blades at which see Fig. B.1. the highest stresses caused by ice loads occur are the A typical parabolic tetrahedron mesh of a propeller fillet at the root of the blade in the case of all propeller blade used in the verification studies is presented in types and the section next to the tip load area in the case of skewed propellers. Fig. B.2a and Fig. B.2b as an example. The requirement for the finite element model is that it is able to represent the complex curvilinear geometry and the thickness variation of the blade and also the C. Boundary Conditions geometry of the fillet at the root of the blade, in order The boundary conditions of the blade model shall be to represent the complex three-dimensional stress state considered at an adequate distance from the peak of the structure and to represent the local stress con- stress location in order to ensure that the boundary centration needed to assess the fatigue strength of the condition has no significant effect on the stress field structure. used in the stress analysis. The interface between The stress of the propeller blade is dominated by bend- blade and hub is not a rigid connection; it is a kind of ing, leading to non-constant stress distribution in the resilient mounting which will be neglected when a thickness direction of the blade. Therefore, more than fixed boundary condition is considered. three elements representing larger thicknesses should Due to the rotation symmetry of the propeller geome- assure a proper representation of the stress distribution. try, the model can be reduced to one blade as illustrated in Fig. B.3. The cut surfaces of the hub shall be coupled by multiple point constraints in such a way B. Good Engineering Practice for FE Analysis that the relative deformations between both surfaces in cylindrical coordinates are prevented. The use of solid elements is highly recommended for determining the stress distribution of the propeller Applied pressure loads blades. The use of parabolic tetrahedron elements (called TET 10) is recommended with reasonable as- The loads are applied as a surface pressure on the pect ratio. An aspect ratio of about 1,5 is recommend- finite element model. This ensures a normal direction ed. Linear and Parabolic hexahedron solid elements of the load towards the curved blade surface. Chapter 22 Annex B C Quality Requirements for FEM Analysis I - Part 1 Page B–2 GL 2008

Fig. B.1 Intersection of propeller blade with typical bending stress distribution in blade thickness direction I - Part 1 Annex B C Quality Requirements for FEM Analysis Chapter 22 GL 2008 Page B–3

Section 5

Section 4 Section 1

Section 3 Section 2

Section 1 Section 2

Section 3 Section 4

Chapter 22 Annex B C Quality Requirements for FEM Analysis I - Part 1 Page B–4 GL 2008

Section 5

Fig. B.2a Fine meshing of 25000 elements Cross section 1 & 2 are sufficiently accurate for stress evaluation

Section 1

Section 5

Section 4

Section 3 Section 2

Section 1 Section 2

I - Part 1 Annex B C Quality Requirements for FEM Analysis Chapter 22 GL 2008 Page B–5

Section 3 Section 4

Section 5

Fig. B.2b Fine meshing of 700000 elements Cross section 1, 2 & 3 are sufficiently accurate for stress evaluation

Cut surfaces

Fig. B.3 Boundary condition